Re: SATA RAID 5 Performance

From: Greg Linwood (g_linwoodQhotmail.com)
Date: 09/01/04 

Date: Wed, 1 Sep 2004 21:31:03 +1000

RAID5 certainly isn't designed to perform write operations as fast as
RAID1+0, but then again writes aren't written transactionally to disk on
data volumes (lazy writes) which often mitigates this significantly,
assuming there is a relatively large amount of memory available. RAID5 is a
poor choice for Log files, but not always a bad choice for Data files. Sure,
if you can throw half of your disks at mirroring, RAID1+0 is the way to go,
but RAID5 often cuts the mustard for many small to mid range transaction
processing systems.

Regards,
Greg Linwood
SQL Server MVP

"David G." <david_nospam@nospam.com> wrote in message
news:OK0WIS6jEHA.3724@TK2MSFTNGP11.phx.gbl...
> Lucas Tam wrote:
>> Hi all,
>>
>> I'm in the process of researching a fast disk array for our new
>> database server.
>>
>> I've been looking at SATA RAID 5. I found a review on Tom's Hardware:
>>
>>
> http://www20.tomshardware.com/storage/20040831/sata-raid-controller-18.html
>>
>> A 12 Disk RAID 5 array is only able to handle 6MB/S?! Is that number
>> correct... I belive they're using IOMeter.
>>
>> Assuming I have 6 - 12 fast disks, what type of performance should I
>> expect from a RAID 5 array? Are there any RAID vendors I should look
>> at in particular?
>>
>> Thanks.
>
> RAID 5 has the worst write performance of all RAID options. I don't know
> what figures you read or how they compare to other ATA or SATA
> implementations, but you should know that if your databases are highly
> transactional, then a RAID 5 solution may not be the best choice. You
> may want to purchase a RAID1+0 solution. Even so, you'll likely want
> your OS, Log files, and tempdb on mirrored drives because of their
> increased write performance.
>
> In my experience most RAID 5 arrays have far less than 12 disks. Most I
> have seen use 5 per array.
>
>
> --
> David G.
>

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