Benefits of SAN

Posted on 2011-05-07
Last Modified: 2012-05-11
Hi, friend of mine is quoted around $20k for a SAN kit to be used in a new brokerage.

Are there significant advantages in using SAN versus going with regular 15k rpm drives in a RAID 10 setup?

The office will have two application servers and one database server (2 physical machines + vmware)
Question by:darkbluegr
    LVL 42

    Assisted Solution

    If you're doing vmware then it makes a lot more sense.  A SAN is a redundant piece of equipment that allow one of the servers to fail and have your virtual machines up and running due to shared storage.  Depending on SAN you can perform snapshots, provide better redundnacy, and reduce the number of physical servers.
    LVL 7

    Assisted Solution

    paulsolov pretty much covered it consisely.  

    In your underlying question of "Is this a reasonable expense?"  I'll answer with a "depends" on the uses for the servers.  If you are wanting 24x7 uptime, just the ability to keep going if one server fails, provide storage greater than what fits inside of a standard server box, or to have manageable backups/disaster recovery those things tend to lead someone to consider a SAN over local disks.

    When you say SAN kit? Are they just the SAN disk unit or is it Fibre Channel with extra Fibre Channel cards in the servers too that add to the cost?  If it is ethernet based using iSCSI or NFS then you are using the most cost efficient version of a SAN for a small business.

    In my experience, a SAN did not provide substantial performance over local disk for any single single server only enhanced functionality. (I have purchased and used SANs from Fibre Channel $400,000 down to NAS/NFS based $2,000)
    LVL 55

    Expert Comment

    Can you qualify this bit please - "The office will have two application servers and one database server (2 physical machines + vmware)"

    Does that mean two physical machines running Windows or Linux natively plus a 3rd server running VMware with some guests on it?

    If so the main benefit of a SAN isn't in use - you're not clustering so you don't need shared storage. The minor benefits such as snapshots, remote mirroring, dual controllers probably isn't worth it. You won't get any speed benefit from having a SAN rather than direct attached local disks, in fact it's almost always slower when both have the same number/type of disks as the SAN just adds an extra protocol and bit of wire to hop through.
    LVL 46

    Assisted Solution

    Step back.  A SAN is basically a way to "network" storage to communicate with computer systems and other storage devices.  In as of itself, there is no benefit to doing this except perhaps to a salesperson.  

    What problem are you trying to solve?   I.e, 24x7 data to multiple hosts?  24x7 data to one host, but a really fast way to fail-over in event the host dies or crashes?  How can ANYBODY tell you if this is a good thing w/o knowing what problems you have.

    I suggest that you do some reading, because there is no simple answer.  Example.  Lets say you have 2 systems each with a RAID10.  If the systems are operating independently of each other, and nothing is shared, then the benefit of NOT doing the SAN is $20,000 in your pocket.    Conversely, if both systems are doing a distributed database, and your database software knows how to load balance both hosts, and you have software in place so that both systems can access/modify the shared data w/o walking on top of it, then maybe this is worth the added expense of purchasing what you need to get a distributed database (and modifying your apps to do this).

    There are tons of articles online that describe benefits of a SAN, choose a few, because this is really a complicated issue.  My biggest beef with most of them is that they tend to skip over what somebody must do to redesign their apps, networking, backup software, and infrastructure to take advantage of it all.  Specifically, one just does not "share" a physical or logical disk drive if EITHER host has write access w/o adding a lot of software or even throwing things out and starting over.

    That is because if host A makes a change, and host "B" doesn't get told by host A that a change was made, then if host "B" has some data in cache then it will be using old data.

    So just adding a SAN w/o having a full understanding of how this fundamentally changes how your hosts work with data could very well cause you to spend a lot of money you didn't think you would have to spend in the first place.

    Don't ask about adding a SAN from hardware perspective .. ask if a SAN is a valid means to an end to solve some networking or availability problem.

    Author Comment

    andyalder, apologize for the big delay in responding. meant that all servers will be virtual, hosted on two vmware hosts.

    The vmware images would be saved in the SAN.

    The only requirement from our vendor is to have 15k rpm drives in the SAN for performance reasons, and the main objective is redundancy
    LVL 55

    Accepted Solution

    In other words you want a cluster,  so you need shared storage. You can get an entry level SAN for $20K easily, I'd probably go for SAS attached shared storage since I don't like iSCSI that much - HP P2000 MSA or Dell MD3200 or several others available, you're talking something of the order of $8000 for the box plus HBAs (without any disks in it). Whether you can call it a SAN is debatable but it has all the benefits except limited scalability - 4 host servers generally.

    15K disks for performance isn't quite valid, 20 * 10K disks will be faster than 4 * 15K ones; ask the software vendor how many IOPS they expect, throughput requirement and size of data.

    Author Comment

    thank you very much, all of the feedback in this thread has helped enormously.

    Would a fiber channel interface be a big improvement in the HP P2000?

    I understand that FC will have bigger bandwidth but does it justify the price jump?
    LVL 55

    Assisted Solution

    FC actually has less bandwidth, 6Gb but 4 lanes so effectively 24Gb, not that it matters since 1500MB/s is the most you can get out of one (ignoring cache) and that's fully populated. FC's advantage is that it's more scalable, you can have thousands of hosts in a FC SAN.

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