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  Asked: May 31 2007   11:13 AM GMT
  Asked by: ROWENS0715

RAID Levels on SAN


SQL Server Enterprise Edition, VRAID5, VRAID1, RAID 5, RAID 1, RAID, SAN, SQL Server 2005

When deploying SQL Server 2005 Enterprise whether it is 32-bit or 64-bit versions using a SAN backend, does the Storage Methodologies regarding RAID1 (VRAID1) or RAID5 (VRAID5) change? There are differences of opinions in our organization regarding this issue. From the DBA Standpoint we strive to implement the correct solution using RAID1 or VRAID1 for protection of the data as well as performance. However, the Technical Support personnel are insisting that VRAID5 should be used because ?It is a SAN and the performance benefits are the same for VRAID5 as VRAID1 without incurring the cost of disk drives?.

All the documentation I can find seem to indicate that the methodology of ?how? RAID levels act are virtually the same whether it is on a local DAS or on a SAN. In other words RAID1 and VRAID1 function the same way and offer the same protection and performance. The same would hold true with RAID5 and VRAID5.

Thanks in advance.

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Last Answered: Oct 5 2007  8:32 PM GMT  by Mrdenny


Latest Contributors: carrollthomas


when you say VRAID1 and VRAID5 it sounds like you are talking about an HP EVA san, these sans virtualise all san volumes accross all disks within their own disk group, raid1 is faster than raid5 but not as fast as raid10. Das is fast but non useable by any other server or host as it is connected directly to the 1 server, and you are limited/restriced to not be able to use clustering is required. San is the best connection type also with sql you know it is better to have your logs and databases on seperate volumes, for speed etc..

if performance is a real issue make sure you have an active/active san configuration, set all your fabric speeds to a fixed speed and not auto negotiate, ensure your server has either mpio or some form of secure path app for the san volumes.

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The basic methodligies do not change between local storage and SAN storage. RAID 1 (and RAID 0+1) still has faster for writes then RAID5 as there is no parity to calculate.

This tip on SearchSQLServer.com may help you out.
http://searchsqlserver.techtarget.com/tip/0,289483,sid87_gci1262122,00.html

Denny
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Pressler2904  |   Feb 22 2008  2:33PM GMT

What I would suggest doing here is setting up two RAID (or vRAID) arrays: RAID 1 for the basic OS installation (including SQL Server) and RAID 5 for the data store (or even RAID 6 if your RAID controller supports it…).

The major reason for utilizing RAID levels 5 or 6 is data protection: as alluded to above, RAID 5 (and 6) contain the equivalent of one disk (RAID 5) or two disks (RAID 6) of parity information, used to recreate the contents of a failed disk (or two, in the case of level 6). Performance during a rebuild WILL be degraded / impacted, and the basic operation is slower overall because of the need to calculate parity information (as ref’d above).

RAID 1 (disk mirroring) will also withstand the loss of a disk, but your data protection is compromised until the failed disk is replaced.

Using 2 arrays will allow for better speed (RAID 1) for the OS, while insuring uptime and resiliency (RAID 5) for the data store itself.

In any setup, the RAID disk pack or array will be presented to the OS as a logical volume (a logical disk) as opposed to a physical disk or disks.