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Buying or Improving on Storage/SAN what to look out for ??

  • October 17, 2006 at 2:36 am

    #75076

    Hi All,

     

    I am in the process of looking to upgrade our current SAN storage enviroment, or possibly buy a new one.

    I would like everyone's input as to things to look out for, i.e specs, features...

    From a database/performance point of view, as much information would be appreciated.

     

    Kindest Regards,

    John Burchel (Trainee Developer)

  • October 18, 2006 at 2:29 am

    #666416

    Don't treat the SAN as 1 big lump of disk space....segmenting the SAN into different areas (for data, logs, temp files, etc) would be advantageous in terms of performance.

  • October 18, 2006 at 12:37 pm

    #666611

    WOW !!! So much to ask ... This first set of questions should be asked right off:

    • How many Tb of storage do you have now ?
    • How many Tb of storage do you need to add ?
    • At what rate is your SAN storage use growing inTb ?
    • How many Tb of SAN storage can you add ?
    • How many servers use your SAN ?
    • How many fiber switches do you have ?
    • Are your fiber switches Brocade or Cisco ?
    • Do your servers connected to the SAN have dual HBAs ?
    • Does your current SAN have DUAL storage processors ?
    • How many Gb of SAN disk cache do you have presently in your SAN ?
    • How many more Gb of SAN disk cache can you add ?
    • Is your SAN configured for 'dual' channels and 'dual' paths ?
    • Does your SAN support SATA disks in addition to SCSI ?

    Now a bit of 'general' SAN stuff:

    • SAN cabinet dedicated to disks can have 10-13 shelves.
    • A shelf of disks can vary in size from 1/2 Tb to 1 1/2 Tb depending on disks and RAID configuration.
    • RAID 5 is more economical than RAID 10 or RAID 1+0.
    • Meta LUNs are better than just LUNs.
    • EMC is the most expensive, Hitachi is 30-40% less, depending ...
    • Hire a consultant if you do not have a good/great SAN Admin.

    And few other relevant 'bits':

    • You'll need different disks - speed and capacity.

    • 15k rpm for transaction logs
    • 10k rpm for database data
    • 7200 rpm SATA for backups

  • These 'different' disks should be segregated by shelf.
  • Spread yout RAID arrays across an entire shelf.
  • Every other disk shelf should have a 'hot spare' disk.

    • and the most important point:

    • Purchase the best support possible - I cannot stress this enough.

    RegardsRudy KomacsarSenior Database Administrator"Ave Caesar! - Morituri te salutamus."

  • October 18, 2006 at 2:57 pm

    #666654

    Rudy,

    Question - why are you recommending 10K disks for data and 15K for logs - we upgraded our data disks to 15K and noticed a substantial performance increase?

    Regards,

    Harley

     

     

  • October 18, 2006 at 3:34 pm

    #666668

    In most instances upgrading from 10k rpm to 15k rpm disks will buy you a performance increase without doing anything else but changing those disks. Based on your application and database mix maybe 15k rpm disks are warranted. I really do not know. The application, database, server configuration, SAN configuration along with size and user transaction loads all figure into performance. There is really no way to say without getting into way too much for detail. I've just provided a general starting point that has served me well for the last few SANs I've been involved with.

    You generally want your fastest disks for transaction logs since they are written to in real time (the only thing faster is solid state disk). Whereas on your data disks pages are written out in 'batches' by the lazy writer or when additional data cache is needed. As for reading, well SQL Server reads extents (64 Kb or 8 pages) and writes pages (8 Kb).

    These are just starting points. However the suggested mix is a little easier on the budget. Consider this, if a shelf of 15k disks runs 30k and gets you 1 Tb. That same shelf with 10k disks may only cost 20k and give you the same 1 Tb of disk space (or maybe even more). ATA disks are even cheaper and larger than their SCSI cousins. When you start adding shelves of disks to a SAN those 10k's really add up fast. 3 15k rpm shelves, 3 Tb roughly or 4 10k rpm shelves, 4 Tb roughly and some change.  But if you can afford 15k rpm disks all around, then go for it (we tried but the cost was huge for number of Tb we had to upgrade additional Tb that we needed to add).

    RegardsRudy KomacsarSenior Database Administrator"Ave Caesar! - Morituri te salutamus."

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