Questions about VERY large software raid config

Hello,

I am currently testing switching from Dell PERC hardware RAID cards to
Linux software RAID and I wanted to see if anyone out there has anything
this large or larger and can give me some tips.

Basically I'm going to do a bunch of RAID1 mirrors (56 drives), RAID)
those in sets of 14 and then stripe those 4 into one big array.  We want
to get the most spindles possible servicing disk requests and I wanted
to know if anyone has tried such a setup.

I have test hardware with 20 drives and it appears to behave nicely and
I'm getting much better throughput from software RAID than the Dell PERC
hardware RAID cards, but I wanted to make sure that this solution would
scale up to 56.  Looking at dmesg (MAX_MD_DEVS=256, MD_SB_DISKS=27) and
looking at the /dev directory (up to 128 SCSI disks) it looks like it
should, but I wanted to get some first hand experience, if there is any
:)

Thanks in advance.

Regards,
Andy.

Andrew Rechenberg
Infrastructure Team, Sherman Financial Group

On Fri, 21 Feb 2003, Rechenberg, Andrew wrote:

Basically I'm going to do a bunch of RAID1 mirrors (56 drives), RAID)
those in sets of 14 and then stripe those 4 into one big array.  We want
to get the most spindles possible servicing disk requests and I wanted
to know if anyone has tried such a setup.

How big are your drives?  There's apparently a 2 TiB limit on raid sizes,
there's even someone who has been asking if 12 x 160 or 13 x 160 is
ok(sorry, I don't have an answer for said person)

Mike

Rechenberg, Andrew on Fri 21/02 10:42 -0500:

Basically I'm going to do a bunch of RAID1 mirrors (56 drives), RAID)
those in sets of 14 and then stripe those 4 into one big array.

I'm curious, why aren't you doing a RAID0 stripe of 28 RAID1s instead?
It sounds like you are doing a RAID0 stripe of 4 RAID0 stripes of 14
RAID1s.  Why the extra step, it can only slow you down???