On Wed, Nov 5, 2008 at 8:22 PM, Gregory Stark <stark@xxxxxxxxxxxxxxxx> wrote: > > "Scott Marlowe" <scott.marlowe@xxxxxxxxx> writes: > >> 2008/11/5 Christian Schröder <cs@xxxxxxxxx>: >>> Tomasz Ostrowski wrote: >>>> >>>> This is wrong. RAID5 is slower than RAID1. >>>> You should go for RAID1+0 for fast and reliable storage. Or RAID0 for >>>> even faster but unreliable. >>>> >>> >>> I did not find a clear statement about this. I agree that RAID10 would be >>> better than RAID5, but in some situations RAID5 at least seems to be faster >>> than RAID1. >> >> For certain read heavy loads RAID-5 will beat RAID-1 handily. After >> all, from a read only perspective, a healthy RAID-5 with n disks is >> equal to a healthy RAID-0 with n-1 disks. > > Uhm, and for a read-heavy load a RAID-1 or RAID 1+0 array with n disks is > equal to a healthy RAID-0 with n disks. Don't know what testing you've done, but very very few RAID-1 / RAID-10 setups can equal a RAID-0 setup of the same number of disks. > RAID-5 should never beat any combination of RAID-0 and RAID-1 with the same > number of drives at read performance. It's advantage is that you get more > capacity. Of course it won't beat a RAID-0 with the same number, but a good controller is just one disk behind a RAID-0 and RAID-1 controllers usually don't aggregate RAID-1 reads, but do allow multiple readers to hit different disks for better concurrent access. But that's not what I was talking about. -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
