Re: RAID Levels

Harry Boswell <hboswel1_at_bellsouth.net> schreef in berichtnieuws n8s8hvk023ge2knlofkg1o4gkkhpr2kp6d_at_4ax.com...
| On Tue, 15 Jul 2003 14:52:55 GMT, Brian Peasland
| <dba_at_remove_spam.peasland.com> wrote:
|
| >The term "level" when dealing with RAID, IMO, is a misnomer. This tends
| >to mean that one level is "higher" than another. But I digress...
| >
| >RAID 0 is not true RAID in that it does not provide any redudancy. It
| >only stripes the data across multiple disk volumes.
| >
| >RAID 1 performs mirroring. It makes a duplicate. RAID 1 is pretty good
| >for write intensive software like Oracle.
| >
| >Many people prefer the redundancy of mirroring, coupled with the speed
| >of striping so they combine RAID 0 and RAID 1 to get RAID 0+1. This may
| >be what you are referring to as RAID 10.
| >
| >The downside of any RAID 1 implementation is that requires twice as much
| >disk. But you get great performance. To save on disk, many people like
| >RAID 5. RAID 5 stripes the data across multiple volumes and it stores
| >parity bits on the disks as well to help with redudancy. RAID 5 does
| >suffer from a write penalty. Your write operations can take twice as
| >long. So many DBAs stay away from RAID 5 if at all possible.
| >
| >RAID 3 is similar to RAID 5 in that it stripes and stores parity bits.
| >But the parity bits are stored on a special volume. So the write
| >performance isn't as bad as RAID 5.
| >
|
| So, if I'm currently running RAID-5, but am about to upgrade and
reconfigure
| my servers, I would benefit by going to RAID-1? Any rules of thumb of how
| much improvement I would see?
|
| Thanks,
| Harry Boswell
|

No, not necessarily. As always: it depends so much on the applications behaviour.
I have read examples where a read-intensive application performs better on RAID-5 then RAID-1.
Writing on a RAID-5 is expensive (for the calculation and additional writes for the parity).
Sorry, don't remember the explanation behind it nor where I read it. Received on Tue Jul 15 2003 - 16:51:43 CDT