Re: RAID5 for Oracle 7.3 on NT 4

Tony Adolph wrote:
>
> Hello All,
>
> I have three questions to ask:

[Other questions SNIPPED]

I have only one answer to give:

> 3) Is it possible to build a stripe set across, say, 3 disks and then
> mirror these 3 disks to give data protection rather than use RAID5.
> The reason for the question is that I have read that RAID5 is quite
> slow for writes and our application is write intensive.

Note that there are two ways to combine stripe (RAID0) and mirror (RAID1). If you build two stripe sets and mirror one to the other it is known as RAID01 or RAID0+1. If you build N mirrored pairs and stripe these this is known as RAID10 or RAID1+0. Performance wise they are usually equivalent but in terms of recovery, safety and reliability there is a world of difference.

In the case of RAID01 you are at risk of catastrophic data loss if, during recover, a second drive fails from the opposite side of the mirror. Recovery time is greater than for RAID10 because the entire stripe must be recovered rather than a single drive which increases the window during which you are at risk of catastrophic loss. Also with RAID01 recovery all drives of the remaining stripe are being actively read to rebuild the damaged stripe set so performance degradation can be as high as 80% of capacity depending on how much priority the RIAD subsystems are giving to data retrieval over recovery which may or may not be configurable.

With RAID10 you are only at risk of catastrophic data loss if the exact single drive mirroring the damaged drive fails which is less likely than the possibility that any of the N drives in a RAID0 mirror will fail. In addition since only that single drive needs to be recovered then recovery is faster reducing the window of risk. Also as intimated above the performance degradation is only a maximum of 80% of the capacity of the one drive pair being recovered not the entire array.

Take a look at RAID controllers from ICP Vortex which implements RAID levels 0, 1, 4, 5 and 10 reportedly have great performance and are certified for most OS's including NT and Linux. Their WEB site is: http://www.icp-vortex.com/ which is a multilingual site BTW.

Art S. Kagel Received on Wed May 12 1999 - 10:24:47 CDT