Disk 100% busy

[Dan Nelson]

In the last episode (Nov 03), Francisco Reyes said:
> On Thu, 3 Nov 2005, Chuck Swiger wrote:
> How about for database? In particular postgresql.
> How bad would RAID 5 be for it?
> 
> I still have some, limited, hopes I can convince the owner of the
> company to go with RAID 10 with 10K rpm drives.. the most likelyhood
> we will go with RAID 5, 7200rpm drives for a database project ahead.
> Alternatively I will see how RAID 5 with 10K rpm SCSI drives compares
> price wise, but I am sure it will be substantially more. :-(

The biggest reason for going RAID-5 is that you only get 50% useable
capacity out of RAID 10, and at least 75% out of a RAID 5 (with a 3+1
layout.  With an 8+1 layout you get 88%).  If you don't need fast
writes, or your controller has sufficient cache to mask the write
penalty, RAID 5 sure holds a lot more data on the same disks.

Always keep your logs on a separate mirrored set of disks, of course.

-- 
	Dan Nelson
	dnelson at allantgroup.com