Re: RAID-5 vs. Disk Mirroring

In article <4e6fus$7i7_at_crchh327.rich.bnr.ca>, Brand Hilton <brand_at_bnr.ca> wrote:

Striping out performs RAID 5, but doesn't have the fail-safe advantages unless you mirror the stripe volumes. Striping costs more - more disks, but RAID 5 has a significant write penalty due to the need to write the parity information across the disks.

Oracle files like REDO logs which are written sequentially don't get any performance boost from a RAID or striped system. They are best on their own, mirrored drive.

I have a mix in my database of striped and mirrored volumes. I may go RAID 5 if I can't afford 2x disks for added storage.

If you go RAID 5, get a controller which has a large write cache. Ours has a 32mb write cache - someone told me that 64mb was needed to cancel out the write penalty of RAID 5.

Brad, I'd love to see the information you gathered.

Glenn Stauffer
DBA
Swarthmore College

>
>Seriously, RAID-5 is a better system than disk mirroring (which is
>RAID-1, if I remember correctly). You should see better performance
>out of a RAID-5 system than you would out of a single disk or a RAID-1
>system. Think about it. Data transfer rate from a disk is limited by
>the spindle speed of the disk. If you have one byte spread across 8
>disks, each rotating at 7200 RPM, that's an effective spindle speed of
>almost 60,000 RPM! Of course, it's not quite that simple, but the
>principle still applies. One added bonus you get with more advanced
>RAID-5 systems is that the size of a logical drive isn't limited by
>the size of your physical drive... add more physical drives and your
>logical drive just gets bigger. RAID-5 is also more expensive, but
>you said that wasn't an object, so RAID-5 all the way!! Some things
>to look for:
Received on Thu Jan 25 1996 - 00:00:00 CET