INTRODUCTION OF SAN
SAN STORAGE:
SAN (Storage Area Network) is storage product of IBM which provides dedicated network to block level data storage.
SANs
are primarily used to make storage devices, such as disk arrays, tape
libraries, and optical jukeboxes, accessible to servers so that the
devices appear like locally attached devices to the operating system.
SAN HISTORY:
1. Internal Storage
- Internal Disks within the Servers
2. Directly Attached (JBOD)
- External Chassis of Disks connected to a Server via a Cable (SCSI or Fiber Channel)
3. Directly Attached Shared
- External Chassis connected to more than one Server via a Cable.
4.
SAN (Storage Area Network)
5.
NAS (Networked Attached Storage)
6. Networked Storage (
NAS +
SAN)
7.
CAS (Content Addressable Storage)
Data centers first created “islands” of SCSI disk
arrays as direct-attached storage (DAS), each dedicated to an
application, and visible as a number of “virtual hard drives” (i.e.
LUNs). Essentially, a
SAN consolidates such storage islands together using a high-speed network.
Operating systems maintain their own file systems on their own dedicated, non-shared
LUNs, as though they were local to themselves. If multiple systems were simply to attempt to share a
LUN,
these would interfere with each other and quickly corrupt the data. Any
planned sharing of data on different computers within a
LUN requires advanced solutions, such as
SAN file systemsor clustered computing.
Despite such issues,
SANs help to increase storage
capacity utilization, since multiple servers consolidate their private
storage space onto the disk arrays. Common uses of a
SAN
include provision of transactionally accessed data that require
high-speed block-level access to the hard drives such as email servers,
databases, and high usage file servers.
Network-attached storage (
NAS ), in contrast to
SAN,
uses file-based protocols such as NFS or SMB/CIFS where it is clear
that the storage is remote, and computers request a portion of an
abstract file rather than a disk block.
SCSI
(sku4ze) Short for small computer system interface, a parallel interface standard used by Apple Macintosh computers, PCs and many UNIX systems for attaching peripheral devices to computers. Nearly all Apple Macintosh computers, excluding only the earliest Macs and the recent iMac, come with a SCSI port for attaching devices such as disk drives and printers. SCSI interfaces provide for data transmission rates (up to 80 megabytes per second). In addition, you can attach multiple devices to a single SCSI port, so that SCSI is really an I/O bus rather than simply an interface.
ATA
(Also known as IDE) is a disk drive implementation that integrates the controller on the disk drive itself. ATA is used to connect hard disk drives, CD-ROM drives and similar peripherals and supports 8/16-bit interface that transfer up to 8.3MB/s for ATA-2 and up to 100MB/s (ATA-6).
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So, what do parallel interfaces have to do with SAS (
Serial Attached SCSI) and SATA (
Serial ATA)? A lot, actually. It is the architectural limitations of the parallel interfaces that serial technologies like SAS and SATA address. In contrast to multiple parallel data stream, data is transmitted serially, that is in a single steam, by wrapping multiple bits into packets and it is able to move that single stream faster than parallel technology.
Serial Attached SCSI (SAS)
Abbreviated as SAS, Serial Attached SCSI, an evolution of parallel SCSI into a point-to-point serial peripheral interface in which controllers are linked directly to disk drives. SAS is a performance improvement over traditional SCSI because SAS enables multiple devices (up to 128) of different sizes and types to be connected simultaneously with thinner and longer cables; its full-duplex signal transmission supports 3.0Gb/s. In addition, SAS drives can be hot-plugged.
Serial ATA (SATA)
Often abbreviated as SATA, Serial ATA is an evolution of the Parallel ATA physical storage interface. Serial ATA is a serial link — a single cable with a minimum of four wires creates a point-to-point connection between devices. Transfer rates for Serial ATA begin at 150MB/s.
Starting with SATA, it extends the capabilities of ATA and offers transfer rates starting at 150MB/s and, after years of development, has moved to the mainstream of disk interfaces. The successor the SCSI interface is SAS at speeds of up to 3Gb/s. Additionally, it also addresses parallel interface issues such as drive addressability and limitations on the number of device per port connection.
SAS devices can communicate with both SATA and SCSI devices (the backplanes of SAS devices are identical to SATA devices). A key difference between SCSI and SAS devices is the addition in SAS devices of two data ports, each of which resides in a different SAS domain. This enables complete failover redundancy. If one path fails, there is still communication along a separate and independent path.
Cables & Connectors
Another big advantage of SATA over ATA is the cabling and connectors. The serial interface reduces the amount of wires needed to transmit data, making for much smaller cable size and making it easier to route and install SATA devices. The IDE cables used in parallel ATA systems are bulkier than Serial ATA cables and can only extend to 40cm long, while Serial ATA cables can extend up to one meter. In addition to the cabling, a new design of connectors is also used that reduces the amount of crosstalk between the wires, and the connector design also provides easier routing and better air flow.
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StarTech's 26-inch Internal SCSI Cable
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StarTech's External SCSI4 Cable
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StarTech's Serial ATA Drive Connection Cable
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StarTech's LP4 to 2 SATA Internal Power Splitter Cable
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| At first glance NAS and SAN might seem almost identical, and in fact many times either will work in a given situation. After all, both NAS and SAN generally use RAID connected to a network, which then are backed up onto tape. However, there are differences -- important differences -- that can seriously affect the way your data is utilized. For a quick introduction to the technology, take a look at the diagrams below. |
 | Wires and Protocols
Most people focus on the wires, but the difference in protocols is actually the most important factor. For instance, one common argument is that SCSI is faster than ethernet and is therefore better. Why? Mainly, people will say the TCP/IP overhead cuts the efficiency of data transfer. So a Gigabit Ethernet gives you throughputs of 600-800 Mbps rather than 1000Mbps.But consider this: the next version of SCSI (due date ??) will double the speed; the next version of ethernet (available in beta now) will multiply the speed by a factor of 10. Which will be faster? Even with overhead? It's something to consider.
The Wires
--NAS uses TCP/IP Networks: Ethernet, FDDI, ATM (perhaps TCP/IP over Fibre Channel someday)
--SAN uses Fibre Channel
--Both NAS and SAN can be accessed through a VPN for security
The Protocols
--NAS uses TCP/IP and NFS/CIFS/HTTP
--SAN uses Encapsulated SCSI | |
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More Differences
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NAS
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SAN
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| Almost any machine that can connect to the LAN (or is interconnected to the LAN through a WAN) can use NFS, CIFS or HTTP protocol to connect to a NAS and share files. | | Only server class devices with SCSI Fibre Channel can connect to the SAN. The Fibre Channel of the SAN has a limit of around 10km at best |
| A NAS identifies data by file name and byte offsets, transfers file data or file meta-data (file's owner, permissions, creation data, etc.), and handles security, user authentication, file locking | | A SAN addresses data by disk block number and transfers raw disk blocks. |
| A NAS allows greater sharing of information especially between disparate operating systems such as Unix and NT. | | File Sharing is operating system dependent and does not exist in many operating systems. |
| File System managed by NAS head unit | | File System managed by servers |
| Backups and mirrors (utilizing features like NetApp's Snapshots) are done on files, not blocks, for a savings in bandwidth and time. A Snapshot can be tiny compared to its source volume. | | Backups and mirrors require a block by block copy, even if blocks are empty. A mirror machine must be equal to or greater in capacity compared to the source volume. |
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What's Next?
NAS and SAN will continue to butt heads for the next few months, but as time goes on, the boundaries between NAS and SAN are expected to blur, with developments like SCSI over IP and Open Storage Networking (OSN), the latter recently announced at Networld Interop. Under the OSN initiative, many vendors such as Amdahl, Network Appliance, Cisco, Foundry, Veritas, and Legato are working to combine the best of NAS and SAN into one coherent data management solution. |
The Benefits of SAS & SATA in Storage
Serial interfaces offer an improvement over older parallel SCSI (with a serial version) in storage applications and environments. These benefits include better performance, better scalability, and also better reliability as the parallel interfaces are at their limits of speed with reliable data transfers. SAS and SATA drives can also operate in the same environment while SCSI and ATA cannot. For example, using faster SAS drives for primary storage and offloading older data to cheaper SATA disks in the same subsystem, something that could not be achieved with SCSI and ATA.
BENEFITS OF SAN TO INDUSTRY:
- Sharing storage usually simplifies storage administration and adds
flexibility since cables and storage devices do not have to be
physically moved to shift storage from one server to another.
- SAN has the ability to allow servers to boot from the SAN itself. This allows for a quick and easy replacement of faulty servers since the SAN can be reconfigured so that a replacement server can use the LUN of the faulty server. While this area of technology is still new many view it as being the future of the enterprise datacenter.
- SANs also tend to enable more effective disaster recovery processes.
- The Fiber Channel over IP (FCIP) and iSCSI protocols have been developed to allow SAN extension over IP networks.
IBM-SAN MODEL:
IBM Categorized as Entry Level (DS3500 Exp, EXP2500 Express,EXP3000),
Midrange (DCS3700,DS5000 series, IBM Storwize V7000 Unified Storage)
and Enterprise (DS8000,IBM XIV, SO
NAS ) Storages based on the data volume of business segment.
DAILY ACTIVITIES OF IBM-SAN ADMINISTRATOR:
Any Administrator commonly work as L1 Support, L2 Support, L3 Support
depending on his experience. Based on his position he will be allocated
with pre-defined privilages and they commonly perform following tasks:
Disk space allocation to various Host
Configuration of the disk
Disk Commissioning
Zoning and Mapping
Archival Solution
Configuration of logical unit numbers (
LUN) to allow systems to perform at optimal level
Back-up and restore
Installs patches or upgrades to the server’s hardware, firmware or software
Perform troubleshooting and performance monitoring of
SAN environment.
Supporting
SAN fiber channel switches
Performing Health Checks on all the
SAN devices in the environment
Storage Administrative tasks like
LUN Allocation, Raid Group Creation,
LUN/Raid Group Expansion,
LUNMigration etc.
HOW SAN LOOKS LIKE?
Click Here To See IBM-
SAN
Can you describe SAN in your won word?
A storage area network (SAN) is a high-speed special-purpose network
(or subnetwork) that interconnects different kinds of data storage
devices with associated data servers on behalf of a larger network of
users. Typically, a storage area network is part of the overall network
of computing resources for an enterprise. A storage area network is
usually clustered in close proximity to other computing resources such
as IBM Power5 boxes but may also extend to remote locations for backup
and archival storage, using wide area network carrier technologies such
as ATM or SONET .
A storage area network can use existing communication technology such as IBM’s optical fiber
ESCON or it may use the newer Fibre Channel technology. Some
SAN
system integrators liken it to the common storage bus (flow of data) in
a personal computer that is shared by different kinds of storage
devices such as a hard disk or a CD-ROM player.
SANs support disk mirroring, backup and restore, archival and
retrieval of archived data, data migration from one storage device to
another, and the sharing of data among different servers in a network.
SANs can incorporate subnetworks with network-attached storage (NAS)
systems.
So you mention NAS, but What is NAS?
Network-attached storage (
NAS) is hard disk storage
that is set up with its own network address rather than being attached
to the department computer that is serving applications to a network’s
workstation users. By removing storage access and its management from
the department server, both application programming and files can be
served faster because they are not competing for the same processor
resources. The network-attached storage device is attached to a local
area network (typically, an Ethernet network) and assigned an IP
address. File requests are mapped by the main server to the NAS file
server.
Network-attached storage consists of hard disk storage, including
multi-disk RAID systems, and software for configuring and mapping file
locations to the network-attached device. Network-attached storage can
be a step toward and included as part of a more sophisticated storage
system known as a storage area network (SAN).
NAS software can usually handle a number of network protocols,
including Microsoft’s Internetwork Packet Exchange and NetBEUI, Novell’s
Netware Internetwork Packet Exchange, and Sun Microsystems’ Network
File System. Configuration, including the setting of user access
priorities, is usually possible using a Web browser.
What is SMTP and how it works?
SMTP (Simple Mail Transfer Protocol) is a TCP/IP protocol used in
sending and receiving e-mail. However, since it is limited in its
ability to queue messages at the receiving end, it is usually used with
one of two other protocols, POP3 or IMAP, that let the user save
messages in a server mailbox and download them periodically from the
server. In other words, users typically use a program that uses SMTP for
sending e-mail and either POP3 or IMAP for receiving e-mail. On
Unix-based systems, sendmail is the most widely-used SMTP server for
e-mail. A commercial package, Sendmail, includes a POP3 server.
Microsoft Exchange includes an SMTP server and can also be set up to
include POP3 support.
SMTP usually is implemented to operate over Internet port 25.
Do you have any idea about NAT?
Short for
Network Address Translation, an Internet standard
that enables a local-area network (LAN) to use one set of IP addresses
for internal traffic and a second set of addresses for external traffic.
A
NAT box located where the LAN meets the Internet makes all necessary IP address translations.
NAT serves three main purposes:
- Provides a type of firewall by hiding internal IP addresses
- Enables a company to use more internal IP addresses. Since they’re
used internally only, there’s no possibility of conflict with IP
addresses used by other companies and organizations.
- Allows a company to combine multiple ISDN connections into a single Internet connection.
Explain DHCP and its uses to an environment?
Short for
Dynamic Host Configuration Protocol, a protocol
for assigning dynamic IP addresses to devices on a network. With dynamic
addressing, a device can have a different IP address every time it
connects to the network. In some systems, the device’s IP address can
even change while it is still connected. DHCP also supports a mix of
static and dynamic IP addresses.
Dynamic addressing simplifies network administration because the
software keeps track of IP addresses rather than requiring an
administrator to manage the task. This means that a new computer can be
added to a network without the hassle of manually assigning it a unique
IP address. Many ISPs use dynamic IP addressing for dial-up users.
What does SNMP stands for?
Short for
Simple Network Management Protocol, a set of
protocols for managing complex networks. SNMP works by sending messages,
called Protocol Data Units, to different parts of a network.
SNMP-compliant devices, called Agents, store data about themselves in
Management Information Bases and return this data to the SNMP
requesters.
What do you know about TCPDump?
TCPdump is a common computer network debugging tool that runs under
the command line. It allows the user to intercept and display TCP/IP and
other packets being transmitted or received over a network to which the
computer is attached. Tcpdump works on most Unix-like platforms: Linux,
Solaris, BSD, Mac OS X, HP-UX and AIX among others. On Windows, WinDump
can be used; it’s a port of tcpdump to Windows.
You must have a root or super user authority to use TCPdumps in UNIX like envrionment.
What is software RAID Levels do?
Redundant Arrays of Independent Disks (RAID) is formally defined as a method to store data on any type of disk medium.
LDAP
The Light Directory Access Protocol (LDAP) defines a standard method
for accessing and updating information in a directory (a database)
either locally or remotely in a client-server model.
What are the benefits of fibre channel SANs?
Fibre Channel SANs are the de facto standard for storage networking
in the corporate data center because they provide exceptional
reliability, scalability, consolidation, and performance. Fibre Channel
SANs provide significant advantages over direct-attached storage through
improved storage utilization, higher data availability, reduced
management costs, and highly scalable capacity and performance.
What environment is most suitable for fibre channel SANs?
Typically, Fibre Channel SANs are most suitable for large data
centers running business-critical data, as well as applications that
require high-bandwidth performance such as medical imaging, streaming
media, and large databases. Fibre Channel SAN solutions can easily scale
to meet the most demanding performance and availability requirements.
What customer problems do fibre channel SANs solve?
The increased performance of Fibre Channel enables a highly effective
backup and recovery approach, including LAN-free and server-free backup
models. The result is a faster, more scalable, and more reliable backup
and recovery solution. By providing flexible connectivity options and
resource sharing, Fibre Channel SANs also greatly reduce the number of
physical devices and disparate systems that must be purchased and
managed, which can dramatically lower capital expenditures.
Heterogeneous SAN management provides a single point of control for all
devices on the SAN, lowering costs and freeing personnel to do other
tasks.
How long has fibre channel been around?
Development started in 1988, ANSI standard approval occurred in 1994,
and large deployments began in 1998. Fibre Channel is a mature, safe,
and widely deployed solution for high-speed (1 GB, 2 GB, 4 GB)
communications and is the foundation for the majority of SAN
installations throughout the world.
What is the future of fibre channel SANs?
Fibre Channel is a well-established, widely deployed
technology with a proven track record and a very large installed base,
particularly in high-performance, business-critical data center
environments. Fibre Channel SANs continue to grow and will be enhanced
for a long time to come. The reduced costs of Fibre Channel components,
the availability of SAN kits, and the next generation of Fibre Channel
(4 GB) are helping to fuel that growth. In addition, the Fibre Channel
roadmap includes plans to double performance every three years.
What are the benefits of 4gb fibre channel?
Benefits include twice the performance with little
or no price increase, investment protection with backward compatibility
to 2 GB, higher reliability due to fewer SAN components (switch and HBA
ports) required, and the ability to replicate, back up, and restore data
more quickly. 4 GB Fibre Channel systems are ideally suited for
applications that need to quickly transfer large amounts of data such as
remote replication across a SAN, streaming video on demand, modeling
and rendering, and large databases. 4 GB technology is shipping today.
How is fibre channel different from ISCSI?
Fibre Channel and iSCSI each have a distinct place in the IT
infrastructure as SAN alternatives to DAS. Fibre Channel generally
provides high performance and high availability for business-critical
applications, usually in the corporate data center. In contrast, iSCSI
is generally used to provide SANs for business applications in smaller
regional or departmental data centers.
When should I deploy fibre channel instead of ISCSI?
For environments consisting of high-end servers that
require high bandwidth or data center environments with
business-critical data, Fibre Channel is a better fit than iSCSI. For
environments consisting of many midrange or low-end servers, an IP SAN
solution often delivers the most appropriate price/performance.
Name some of the SAN topologies ?
Point-to-point, arbitrated loop, and switched fabric topologies.
What’s the need for separate network for storage why LAN cannot be used?
LAN hardware and operating systems are geared to user traffic, and
LANs are tuned for a fast user response to messaging requests.
With a SAN, the storage units can be secured separately from the
servers and totally apart from the user network enhancing storage access
in data blocks (bulk data transfers), advantageous for server-less
backups.
What are the advantages of RAID?
“Redundant Array of Inexpensive Disks”
Depending on how we configure the array, we can have the
- data mirrored [RAID 1] (duplicate copies on separate drives)
- striped [RAID 0] (interleaved across several drives), or
- parity protected [RAID 5](extra data written to identify errors).
These can be used in combination to deliver the balance of performance and reliability that the user requires.
Define RAID? Which one you feel is good choice?
RAID (Redundant array of Independent Disks) is a technology to
achieve redundancy with faster I/O. There are Many Levels of RAID to
meet different needs of the customer which are: R0, R1, R3, R4, R5, R10,
R6.
Generally customer chooses R5 to achieve better redundancy and speed and it is cost effective.
R0 – Striped set without parity/[Non-Redundant Array].
Provides improved performance and additional storage but no fault
tolerance. Any disk failure destroys the array, which becomes more
likely with more disks in the array. A single disk failure destroys the
entire array because when data is written to a RAID 0 drive, the data is
broken into fragments. The number of fragments is dictated by the
number of disks in the drive. The fragments are written to their
respective disks simultaneously on the same sector. This allows smaller
sections of the entire chunk of data to be read off the drive in
parallel, giving this type of arrangement huge bandwidth. RAID 0 does
not implement error checking so any error is unrecoverable. More disks
in the array means higher bandwidth, but greater risk of data loss
R1 – Mirrored set without parity.
Provides fault tolerance from disk errors and failure of all but one of
the drives. Increased read performance occurs when using a
multi-threaded operating system that supports split seeks, very small
performance reduction when writing. Array continues to operate so long
as at least one drive is functioning. Using RAID 1 with a separate
controller for each disk is sometimes called duplexing.
R3 – Striped set with dedicated parity/Bit interleaved parity.
This mechanism provides an improved performance and fault tolerance
similar to RAID 5, but with a dedicated parity disk rather than rotated
parity stripes. The single parity disk is a bottle-neck for writing
since every write requires updating the parity data. One minor benefit
is the dedicated parity disk allows the parity drive to fail and
operation will continue without parity or performance penalty.
R4 – Block level parity.
Identical to RAID 3, but does block-level striping instead of byte-level
striping. In this setup, files can be distributed between multiple
disks. Each disk operates independently which allows I/O requests to be
performed in parallel, though data transfer speeds can suffer due to the
type of parity. The error detection is achieved through dedicated
parity and is stored in a separate, single disk unit.
R5 – Striped set with distributed parity.
Distributed parity requires all drives but one to be present to operate;
drive failure requires replacement, but the array is not destroyed by a
single drive failure. Upon drive failure, any subsequent reads can be
calculated from the distributed parity such that the drive failure is
masked from the end user. The array will have data loss in the event of a
second drive failure and is vulnerable until the data that was on the
failed drive is rebuilt onto a replacement drive.
R6 – Striped set with dual distributed Parity.
Provides fault tolerance from two drive failures; array continues to
operate with up to two failed drives. This makes larger RAID groups more
practical, especially for high availability systems. This becomes
increasingly important because large-capacity drives lengthen the time
needed to recover from the failure of a single drive. Single parity RAID
levels are vulnerable to data loss until the failed drive is rebuilt:
the larger the drive, the longer the rebuild will take. Dual parity
gives time to rebuild the array without the data being at risk if one
drive, but no more, fails before the rebuild is complete.
What is the difference between RAID 0+1 and RAID 1+0?
RAID 0+1 (Mirrored Stripped)
In this RAID level all the data is saved on stripped volumes which
are in turn mirrored, so any disk failure saves the data loss but it
makes whole stripe unavailable. The key difference from
RAID 1+0 is that
RAID
0+1 creates a second striped set to mirror a primary striped set. The
array continues to operate with one or more drives failed in the same
mirror set, but if drives fail on both sides of the mirror the data on
the RAID system is lost. In this
RAID level if one disk is failed full mirror is marked as inactive and data is saved only one stripped volume.
RAID 1+0 (Stripped Mirrored)
In this RAID level all the data is saved on mirrored volumes which are
in turn stripped, so any disk failure saves data loss. The key
difference from
RAID 0+1 is that
RAID 1+0 creates a striped set from a series of mirrored drives. In a failed disk situation
RAID
1+0 performs better because all the remaining disks continue to be
used. The array can sustain multiple drive losses so long as no mirror
loses both its drives.
This
RAID level is most preferred for high performance and high data protection because rebuilding of
RAID 1+0 is less time consuming in comparison to
RAID 0+1.
When JBOD’s are used?
“Just a Bunch of Disks”
It is a collection of disks that share a common connection to the server, but don’t include the mirroring,
striping, or parity facilities that
RAID systems do, but these capabilities are available with host-based software.
Differentiate RAID & JBOD?
RAID: “Redundant Array of Inexpensive Disks”
Fault-tolerant grouping of disks that server sees as a single disk volume
Combination of parity-checking, mirroring, striping
Self-contained, manageable unit of storage
JBOD: “Just a Bunch of Disks”
Drives independently attached to the I/O channel
Scalable, but requires server to manage multiple volumes
Do not provide protection in case of drive failure
What is a HBA?
Host bus adapters (HBAs) are needed to connect the server (host) to the storage.
What are the advantages of SAN?
Massively extended scalability.
Greatly enhanced device connectivity.
Storage consolidation.
LAN-free backup.
Server-less (active-fabric) backup.
Server clustering.
Heterogeneous data sharing.
Disaster recovery – Remote mirroring.
While answering people do NOT portray clearly what they mean & what
advantages each of them have, which are cost effective & which are
to be used for the client’s requirements.
What is the difference b/w SAN and NAS?
The basic difference between SAN and NAS, SAN is Fabric based and NAS is Ethernet based.
SAN – Storage Area Network
It accesses data on block level and produces space to host in form of disk.
NAS – Network attached Storage
It accesses data on file level and produces space to host in form of shared network folder.
What is a typical storage area network consists of – if we consider it for implementation in a small business setup?
If we consider any small business following are essentials components of SAN:
Fabric Switch.
FC Controllers.
JBOD’s.
Can you briefly explain each of these Storage area components?
Fabric Switch: It’s a device which interconnects multiple network
devices .There are switches starting from 16 port to 32 ports which
connect 16 or 32 machine nodes etc. vendors who manufacture these kind
of switches are Brocade, McData.
What is the most critical component in SAN?
Each component has its own criticality with respect to business needs of a company.
How is a SAN managed?
There are many management software’s used for managing SAN’s to name a few:
Santricity.
IBM Tivoli Storage Manager.
CA Unicenter.
Veritas Volumemanger.
Which one is the Default ID for SCSI HBA?
Generally the default ID for SCSI HBA is 7.
SCSI- Small Computer System Interface.
HBA – Host Bus Adaptor.
What is the highest and lowest priority of SCSI?
There are 16 different ID’s which can be assigned to SCSI device 7, 6, 5, 4, 3, 2, 1, 0, 15, 14, 13, 12, 11, 10, 9, 8.
Highest priority of SCSI is ID 7 and lowest ID is 8.
How do you install device drivers for the HBA first time during OS installation?
In some scenarios you are supposed to install Operating System on the
drives connected thru SCSI HBA or SCSI RAID Controllers, but most of
the OS will not be updated with drivers for those controllers, that time
you need to supply drivers externally, if you are installing windows,
you need to press F6 during the installation of OS and provide the
driver disk or CD which came along with HBA.
If you are installing Linux you need to type “linux dd” for installing any driver.
What is Array?
Array is a group of Independent physical disks to configure any Volumes or RAID volumes.
Can you describe at-least 3 troubleshooting scenarios which you have come across in detail?
SCENARIO 1: How do you find/debug when there is error while working SCSI devices?
In our daily SAN troubleshooting there are many management and
configuration tools we use them to see when there is a failure with
target device or initiator device.
Some time it is even hard to troubleshoot some of the things such as
media errors in the drives, or some of the drives taking long time to
spin-up. In such cases these utilities will not come to help. To debug
this kind of information most of the controller will be implemented with
3-pin serial debug port. With serial port debug connector cable you can
collect the debug information with hyper terminal software.
SCENARIO 2: I am having an issue with a controller
its taking lot of time to boot and detect all the drives connected how
can I solve this.?
There are many possibilities that might cause this problem. One of the
reason might be you are using bad drives that cannot be repaired. In
those cases you replace the disks with working ones.
Another reason might be slots you connected your controller to a slot which might not be supported.
Try to connect with other types of slots.
One more probable reason is if you have flashed the firmware for different OEM’s on the same hardware.
To get rid of this the flash utilities will be having option to erase
all the previous and EEPROM and boot block entry option. Use that option
to rectify the problem.
SCENARIO 3: I am using tape drive series 700X, even
the vendor information on the Tape drive says 700X, but the POST
information while booting the server is showing as 500X what could be
the problem?
First you should make sure your hardware is of which series, you can find out this in the product website.
Generally you can see this because in most of the testing companies they
use same hardware to test different series of same hardware type. What
they do is they flash the different series firmware. You can always
flash back to exact hardware type.
Which are the 4 types of SAN architecture types ?
Core-edge.
Full-Mesh.
Partial-Mesh.
Cascade.
Which command is used in linux to know the driver version of any hardware device?
dmesg.
How many minimum drives are required to create R5 (RAID 5)?
You need to have at least 3 disk drives to create R5.
Can you name some of the states of RAID array?
There are states of RAID arrays that represent the status of the RAID arrays which are given below:
Online.
Degraded.
Rebuilding.
Failed.
What are the protocols used in physical/datalink and network layer of SAN?
Ethernet.
SCSI.
Fibre Channel.
What is storage virtualization?
Storage virtualization is amalgamation of multiple n/w storage devices into single storage unit.
Describe in brief the composition of FC Frame?
Start of the Frame locator
Frame header (includes destination id and source id, 24 bytes/6 words).
Data Payload (encapsulate SCSI instruction can be 0-2112 bytes in length).
CRC (error checking, 4 bytes).
End of Frame (1 byte).
What is virtualization?
Virtualization is logical representation of physical devices. It is
the technique of managing and presenting storage devices and resources
functionally, regardless of their physical layout or location.
Virtualization is the pooling of physical storage from multiple network
storage devices into what appears to be a single storage device that is
managed from a central console. Storage virtualization is commonly used
in a storage area network (SAN). The management of storage devices can
be tedious and time-consuming. Storage virtualization helps the storage
administrator perform the tasks of backup, archiving, and recovery more
easily, and in less time, by disguising the actual complexity of the
SAN.
What is HA?
HA High Availability is a technology to achieve failover with very
less latency. Its a practical requirement of data centers these days
when customers expect the servers to be running 24 hours on all 7 days
around the whole 365 days a year – usually referred as 24x7x365. So to
achieve this, a redundant infrastructure is created to make sure if one
database server or if one app server fails there is a replica Database
or Appserver ready to take-over the operations. End customer never
experiences any outage when there is a HA network infrastructure.
Can you name some of the available tape media types?
There are many types of tape media available to back up the data, some of them are:
DLT: Digital Linear Tape – technology for tape
backup/archive of networks and servers; DLT technology addresses
midrange to high-end tape backup requirements.
LTO: Linear Tape Open; a new standard tape format developed by HP, IBM, and Seagate.
AIT: Advanced Intelligent Tape; a helical scan
technology developed by Sony for tape backup/archive of networks and
servers, specifically addressing midrange to high-end backup
requirements.
Can we assign a hot spare to R0 (RAID 0) array?
No, since R0 is not redundant array, failure of any
disks results in failure of the entire array so we cannot rebuild the
hot spare for the R0 array.
Name the features of SCSI-3 standard?
QAS: Quick arbitration and selection.
Domain Validation.
CRC: Cyclic redundancy check.
What is Multipath I/O?
Fault tolerant technique where, there is more than one physical path
between the CPU in the computer systems and its main storage devices
through the buses, controllers, switches and other bridge devices
connecting them.
What is disk array?
Set of high performance storage disks that can store several
terabytes of data. Single disk array can support multiple points of
connection to the network.
What are different types of protocols used in transportation and session layers of SAN?
Fibre Channel Protocol (FCP).
Internet SCSI (iSCSI).
Fibre Channel IP (FCIP).
What is the type of Encoding used in Fibre Channel?
8b/10b, as the encoding technique is able to detect all most all the bit errors
What are the main constrains of SCSI in storage networking?
Deployment distance (max. of 25 mts).
Number of devices that can be interconnected (16).
What is a Fabric?
Interconnection of Fibre Channel Switches.
What are the services provided by Fabric to all the nodes?
- Fabric Login.
- SNS.
- Fabric Address Notification.
- Registered state change notification.
- Broadcast Servers.
What is the difference between LUN and WWN?
LUN: Unique number that is assigned to each storage device or partition of the storage that the storage can support.
WWN: 64bit address that is hard coded into a fibre channel HBA and
this is used to identify individual port (N_Port or F_Port) in the
fabric.
What are the different topologies in Fibre Channel?
- Point-to-Point.
- Arbitrary Loop.
- Switched Fabric Loop.
What are the layers of Fibre Channel Protocol?
- FC Physical Media.
- FC Encoder and Decoder.
- FC Framing and Flow control.
- FC Common Services.
- FC Upper Level Protocol Mapping.
What is zoning?
Fabric management service that can be used to create logical subsets
of devices within a SAN. This enables portioning of resources for
management and access control purpose.
What is the purpose of disk array?
Probability of unavailability of data stored on the disk array due to single point failure is totally eliminated.
How does FC Switch maintain the addresses?
FC Switch uses simple name server (SNS) to maintain the mapping table.
What are the two major classification of zoning?
Two types of zoning are:
- Software Zoning.
- Hardware Zoning.
What are different levels of zoning?
- Port Level zoning.
- WWN Level zoning.
- Device Level zoning.
- Protocol Level zoning.
- LUN Level zoning.
What are the 3 prominent characteristics of SAS Protocol?
- Native Command Queuing (NCQ.)
- Port Multiplier.
- Port Selector.
What are the 5 states of Arbitrary Loop in FC?
- Loop Initialization.
- Loop Monitoring.
- Loop arbitration.
- Open Loop.
- Close Loop.
What is LUN Masking?
A method used to create an exclusive storage area and access control.
And this can be achieved by storage device control program.
What is snapshot?
A snapshot of data object contains an image of data at a particular point of time.
What is hot-swapping?
Devices are allowed to be removed and inserted into a system without turning off the system.
