Six SAN shoot-out

Six SAN shoot-out

Summary: Managing data storage is just as much of a task (or greater) as managing the servers themselves. It makes sense to centralise management in larger organisations wherever possible. Enter the storage area network (SAN).

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Managing data storage is just as much of a task (or greater) as managing the servers themselves. It makes sense to centralise management in larger organisations wherever possible. Storage area network (SAN) technology enables a network of physical storage devices to be managed as a single unit. They can then be readily divided into a number of logical drives.

Basic SANs use either Fibre Channel (FC) or iSCSI technology. iSCSI runs over standard gigabit Ethernet networks using software to support the SAN infrastructure, whereas FC devices are much faster but require specialised hardware such as optical fibre cabling and FC switches.

  iSCSI Fibre Channel
Positive
  • Works over current Ethernet network
  • Don't need expensive FC switches or hosts FC HBA
  • Can remotely access storage via TCP/IP
  • Up to 4Gbps transfer speed
  • Better redundant performance
Negative
  • Transfer speed is only up to 1Gbps
  • In some cases there may be the need to share bandwidth with a host's general TCP/IP
  • Needs special hardware
  • Only connects locally within the constraints of an FC network

SAN vs. NAS

Storage area networks and network attached storage (NAS) are similar names and easily confused. The key differences are:

  • The manner in which stored information is presented to servers. Data stored in a NAS will be seen on a non-local drive whereas data stored on a SAN appears to reside in a local drive.
  • Physical hardware. A NAS is a single storage device, whereas a SAN is a centralised collection of networked storage devices. Multiple servers could require an individual NAS each, but a SAN allows sharing of a single storage area.
  • Administration. SAN space can be allocated as needed to each server, often on-the-fly. Administrators can determine a total amount of physical drive space required without concerning themselves with how to physically allocate space to each server.
  • A NAS is optimised for sharing while a SAN is optimised for speed and capacity.

Comparison of NAS and SAN (Credit: Enex TestLab/CBS Interactive)

NAS/SAN hybrids are also possible where one or more partitions in the SAN are provided with a NAS gateway.

Storage clustering

Storage clustering is a method of combining networked storage devices to form a single virtual device. It allows the creation of large, redundant storage arrays which remain relatively easy to manage. Since clustered systems contain multiple disks, each with its own read-write head, performance can potentially be multiplied by simultaneously accessing multiple physical devices.

RAID

Available in a variety of flavours, Redundant Array of Independent (or Inexpensive) Disks (RAID) is a method of combining several physical drives into a single logical unit with varying levels of data redundancy. The most commonly seen varieties are 0, 1, 5, 6, 10, 50 and 60. RAID 0 (also called striping) connects several identically sized volumes together, increasing read and write speed but offering no redundancy. RAID 1 (also called mirroring) is a 1:1 copy of a disk, so if one disk fails, there is a redundant copy — it should increase read speeds, but has a penalty on writes and can be costly — for every disk you wish to protect, you must purchase an additional identical capacity disk.

RAID 5 and 6 are the compromise — both allow a collection of disks of identical capacity to be connected together to form a single logical unit, but rather than the expense of having to purchase a drive per drive you wish to protect, they spread the parity data across all the disks in the array. RAID 5 can survive a single drive failure, RAID 6 can survive two.

RAID 10, 50 and 60 are combinations of RAID 0 plus RAID 1, 5 or 6. Some SAN vendors support non-standard RAID varieties or less common standards such as RAID 3 or 4.

Thin provisioning

Consider an organisation where data storage is shared equally between two servers. If one server is discovered to use its virtual disk space faster than the other, it may be necessary to purchase more drives to satisfy the capacity needs of this space-hungry server even though there is still storage space available on the other server. Thin provisioning is a method of allocating available space to each virtual drive as needed. This has the potential to save organisations from purchasing vast amounts of hardware that may never be fully utilised.

Topics: Dell, EMC, Hewlett-Packard, IBM, Storage

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5 comments
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  • Where's the testing?

    I see Enex was involved, but I don't see the results of any testing.

    At the moment it looks more like "Heres six SAN devices and a summary of their spec sheets".

    Having details of how these devices would be good - particularly when the device comes in multiple configs. We have the MD3000, seeing it compared to a MD3000i would be useful.
    anonymous
  • slight correction

    Oops. Missed a word in there:

    Second last sentence should read:
    "Having details of how these devices *perform* would be good - particularly when the device comes in multiple configs. "
    anonymous
  • HDS?

    Where is HDS in all of this...

    These aren't SAN's they're over powered disk storage platforms.

    Call them SAN's when you looking at at least the AMS2000, or USP/V/VM level.
    anonymous
  • where I work, We assemble this model!!!
    jais86
  • Dell PowerVault MD3000i iSCSI SAN

    I'm not a huge IT guy, I'm a marketing guy that is part owner of a small, nationwide company that deals with, and uses a lot of computer stuff (I'm not going to tell you the name of the company, because I don't want you to think this is a lame way to get our link up)

    I was worried, that, even though it was a lot of money for ME, its not the most expensive solution, so I was afraid of its reliability, and expand ability, I've had it for a year now, and it is just amazing.

    I rarely write reviews, and am always skeptical when reading one, but I HAD to write this one, because it's funny, and a true testament to this Powervault...More reviews need to look like this, if I do say so myself, and I'll be sharing this on different forums. ;)

    I recently had a tech come into our offices to run some wires, setup a couple things, etc., He's one of those computer snobs. Knows everything about computers, He was constantly sarcastically joking about EVERYTHING in our offices, from our fax machines, to our computers, I think he even said something negative about my cell phone! I just assumed it wouldn't have mattered what model I had, he would have hated it. (this is kind of how I see online reviews. It's a metaphor. There will ALWAYS be more motivation for someone to post a negative experience than a positive one- in fact, the default attitude, online- is negative.)

    However, when he started working with my new (new to me, but used) Dell PowerVault MD3000i He actually COMPLIMENTED me on it! He talked about how others are overpriced, and how this one was expandable, etc. It was just funny, because I thought, "maybe he just realized he's been so negative, and wanted to make up for it by saying something positive."

    But RIGHT after he complimented me on the Dell PowerVault MD3000i he said..."Man, the lighting in here sucks! Your fluorescent lighting have different color temps. How do you work in here?!"

    Thats when I knew his Dell PowerVault MD3000i compliment was genuine! :) LOL
    radiationcomputerstation.com