[CentOS] RAID5 or RAID50 for database?

Sun May 25 10:18:57 UTC 2008
Christopher Chan <christopher at ias.com.hk>

> Ok, so it stripping a mirror more redundant then, from what you say? 
> But, it's limited to pairs of 4 HDD's, which means a bigger chassis, and 
> a mobo / PCI controller that can support 8 HDD's if I want to add more?

Huh? Said who? 6 disks = 3 mirrors = 3 stripped mirrors or 3 x single 
disk speed.

> But, if I want to use 6+ drives, rather use RAID 6? How does RAID-6 
> perform in relation to RAID-5 or RAID-10 (RAID-01)?

No comments on RAID10...the new md raid10 module from Neil Brown is not 
available on Centos 4 and I do not know how that modules handles 6 disks.

However, using raid 0+1 as neil calls it, with 6 disks you get three 
mirrors that are stripped giving you the possibility of surviving three 
disk failures provided that they are all from different arrays but you 
will also lose the everything if the disks of any one mirror fail.. 
RAID6 gives you the maximum of surviving any two disk failure. I have 
heard of horror stories with md raid5 and besides, with 6 disks you 
would be better off using a hardware raid card that supports a bbu cache 
like 3ware 9550 and above to cut down on the data traffic over the bus 
if you want raid5/6.