2850 drive bays not hot-swap?

[Brett Dikeman]

On Jan 24, 2008 3:35 PM, William Warren
<hescominsoon at emmanuelcomputerconsulting.com> wrote:
> i'm curious why you aren't using the raid card?

Simplicity, familiarity, standardization, and better OS integration
and monitoring.

Sure, I lose the battery-backed write cache some cards have, and I
lose is the continuous verify the Dell controllers perform.  If you
want to come close to the latter functionality with linux md, you can
do it quite easily by setting a very low minimum rebuild rate and
regularly kicking off a verify via cron.

Performance is fine with linux md (I'm using RAID1 and 10, didn't
think to benchmark RAID5), and interestingly enough- Solaris ZFS
RAID-Z across 5 drives was around 185 MB/sec whereas the PERC
controller with 4 drives in RAID0 ran out of steam around the 100
MB/sec mark.

hdparm's timed buffered disk reads on the md devices yield 100 MB/sec
for the 4-drive RAID10 array, and the RAID1 array clocks in at 73
MB/sec.  Write on the RAID10 with dd (from /dev/zero to a 50% full xfs
filesystem with 900,000 files, mounted
rw,noatime,nodiratime,logbufs=8) yields about 78 MB/sec; a dd read (to
/dev/null) is 148 MB/sec.  Bonnie++ on the RAID10 yielded 77.5 MB/sec
write, 119 MB/sec read.

>  Hotswap under linux software raid isn't totally automatic IIRC.

Certainly, but I don't need pop-a-drive-in-and-done automatic
rebuilds.  What I do need, however, is to be able to swap the drive
out, repartition the new one, and add it back into the array without
rebooting, especially since this machine takes something like 5+
minutes to boot.  That's 1/6th the time it takes to rebuild my system
mirror :-)

>  here's a link from the archives HTH.
> http://lists.us.dell.com/pipermail/linux-poweredge/2003-July/008898.html

Ah!  Very nice, those /proc pokes were exactly what I was looking for;
thank you! (haven't tried it yet, but I will.)  That email also
reminded me that I forgot to set up the bootloader on the second
drive; I did remember /boot (and everything else lives in LVM on top
of the RAID device.)

Brett