Re: Best use of second controller with faster disks?

Vivek Khera writes:

> what raid card have you got?

2 3ware cards.
I believe both are 9550SX

> i'm playing with an external enclosure
> which has an areca sata raid in it and connects to the host via fibre
> channel.

What is the OS? FreeBSD?
One of the reasons I stick with 3ware is that it is well supported in
FreeBSD and has a pretty decent management program

> it is wicked fast, and supports a RAID6 which seems to be
> as fast as the RAID10 in my initial testing on this unit.

My next "large" machine I am also leaning towards RAID6. The space different
is just too big to ignore.
3ware recommends RAID6 for 5+ drives.

> What drives are you booting from?

Booting from the 8 drive raid.

> If you're booting from the 4-drive
> RAID10, perhaps split that into a pair of RAID1's and boot from one
> and use the other as the pg log disk.

Maybe for the next machine.

> however, I must say that with my 16 disk array, peeling the log off
> the main volume actually slowed it down a bit. I think that the raid
> card is just so fast at doing the RAID6 computations and having the
> striping is a big gain over the dedicated RAID1 for the log.

Could be.
Seems like RAID6 is supposed to be a good balance between performance and
available space.

> Right now I'm testing an 8-disk RAID6 configuration on the same
> device; it seems slower than the 16-disk RAID6, but I haven't yet
> tried 8-disk RAID10 with dedicated log yet.

Is all this within the same controller?

> i'd bump checkpoint_segements up to 256 given the amount of disk
> you've got dedicated to it. be sure to increase checkpoint timeout too.

Thanks. Will try that.