On Sun, Mar 22, 2009 at 1:08 AM, Arun Khan <[email protected]> wrote:
> Has anyone done a 0+1 SW RAID?

I had similar setups a few years ago when Linux did not have
native raid10 support.  So I had to create two raid1 devices
and then stripe them with a raid0 device on top.

My setup worked well enough for me to put into production use,
and I think they are still running.

Instead of layering multiple raid levels, new Linux kernels offer
native raid10 support.  I have not used this, it would be good
to research this further before making a decision.


> I am thinking of configuring 2 disks (sda+sdc) in a RAID0 setup and then
> mirror this RAID device on the other 2 disks (sdb+sdd).

Do not do it this way.  If a single disk fails, the rebuild will take
too long.  Better way to setup is like this:

md0 = raid1 sda+sdc
md1 = raid1 sdb+sdd
md2 = raid0 md0+md1
mkfs on md2

In case of sda failure, only sda+sdc need to be re-synced.

Doing it your way will mean that md0 and md1 need to be
re-synced and will take double the time.


Note that as long as you are not doing RAID parity computation,
as in RAID5/6, SW raid has absolutely no CPU hit.  SW RAID0/1
are all good in my book.

- Raja
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