[Beowulf] RAID for home beowulf

Mark Hahn hahn at mcmaster.ca
Sat Oct 3 15:49:20 PDT 2009

> because parity has to be calculated and written to the disk. In fact this 
> performance penalty has lead to a campaign against RAID5:
>  http://www.baarf.com/

redundancy costs - your only choice is what kind of redundancy you want.
raid5 has its issues, but really what's needed is redundancy managed 
by the filesystem.  doing it block-level is what introduces the pain.

>> 3) I'll leave the /boot partition on one of the 3 disks and it will NOT
>> be included in the RAID array, is this ok?
> I think you'd be better off putting your system one one of your three disks, 
> and making a RAID1 for /home from the other two. This will give you a

I disagree.  for one, I strongly advice against partition-o-philia:
the somewhat traditional practice of putting lots of separate partitions
on a system.  but for 3 disks, linux MD has a nice mode where each block
is stored twice.  so you get 2/3 space efficiency and potentially better

> It works, and you do get HA, but performance is not good. I'm now simplifying 
> and upgrading the systems by fitting a 3ware 8006-2 hardware RAID1 controller 
my experience with old 3ware boards was quite poor performance - much 
slower than MD.  >= 95xx are respectable, though.

> One thing you need to bear in mind in relation to HA is that software RAID 
> does not support hot-swap - That's why I chose the 3ware 8006-2, which is not 
> very expensive. It doesn't automatically detect new disks and rebuild the 
> RAID, but it does support hot-swap and has a web GUI:
>  http://www.3ware.com/products/serial_ata8000.asp

MD software raid certainly can support HS - it's mainly a feature of the 
controller.  (this is not to say that most controllers do HS well.)

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