[Linux-HA] Raid and drdb

[Dimitri Maziuk]

On Monday 27 July 2009 12:14:57 Claus Denk wrote:
> Hi all,
>
> we have now almost configured our hardware for a HA cluster. We will use
> two IBM 3550 M2 servers, and I would like to ask you if you could share
> some experience about different disk configurations.
>
> 1) Using drdb, is having some hardware RAID on both machines good
> practice (for example 3 disks with RAID 5) or is it not necessary to do
> so as drdb is our network raid? I guess in case of failure of the drdb
> communication it would be good to have some additional raid security on
> each server. Does it affect the write performance a lot?

<mee too>
Actually, I'd like to know: what happens when a disk fails? Would that 
propagate to DRBD and trigger a failover?

> 2) This machine has a maximum of 4 SAS slots, what would be good
> practice to install OS and data (2+2 disks with raid 1, or everything on
> 3 disks raid 5, o 4 disks raid 10?) Of course disk price is an issue, we
> would like to have 500 GB of data, which requires 3 300 Gb disks for raid
> 5.

With SAS drives you should be OK with raid 5 (SATA is where you'l want raid 
1/10, apparently). Personally, I wouldn't worry too much about raid'ing the 
root drives: HA cluster should give you enough time to reinstall the OS if 
one fails. I would keep a spare disk handy.

Dimitri
-- 
Dimitri Maziuk
Programmer/sysadmin
BioMagResBank, UW-Madison -- http://www.bmrb.wisc.edu