Re: asm on san
Date: Thu, 18 Dec 2008 03:53:34 -0800 (PST)
My experiances in the last 8 yrs of the Enterprise storage environment do not bear out the anti RAID 5 people. RAID 5 is used extensively in this financial services environment. We have an envionment which Michael Austin, Palooka and others have described. SAN and the storage is a service provided to us with guaranteed throughput, response time and availability. We make use of what was at one time the biggest SAN in europe (apparently ... I never measured it...). There are thousands (well at least 2000..) of servers connected to SAN fabrics spanning two datacentres linked by DWDM links. The storage devices are HDS and we are currently using the USP v model configured using maximum cache. The performance is staggering - the only bottleneck we ever see is over the fabric and through that we can happily sustain a tablescan rate of 700MB/s. All of these storage devices are configured using RAID 5. A few years ago we used to insist on RAID 10 for redo/archive, but no testing we did using oracle's ORION tool (which is ace) could show any benefit and now its all RAID 5.
There are many reasons why RAID 5 is good and often the only practicle choice. You get more data on to your disks compared to RAID10 - and when you have many petabytes of storage to manage the importance of this cannot be overstated. Less disks means less floorspace in the datacentre, less cooling and less power consumption. These can be critical issues when you consider the explosion of data storage requirements over the last few years. I would just get laughed at if I demanded RAID 10 ... especially where no emprical performance test can justify it.
Now clearly, if you are not in that environment, or one like it, and only have direct attatched storage with a miniscule cache to work with , or a cheapo SAN attatched storage device without the necessary cache then RAID10 will beat RAID5 hands down, but I think it is important to point out that there clearly is a place for RAID 5 with Oracle, and sweeping statements along the lines of "never use RAID 5 for oracle databases" are untrue. Whilst BAARF certainly was correct in its day - its now old skool - things move on.
Ralph Received on Thu Dec 18 2008 - 05:53:34 CST