[TriLUG] general RAID questions
Joseph Mack NA3T
jmack at wm7d.net
Sun Nov 27 12:39:31 EST 2011
I've just worked through the RAID section of Alan Porter's
Jan presentation this year.
I've not done any RAID and have these questions.
o is software raid the default in linux?
with hardware RAID a light on a failed drive comes on.
Presumably the hardware driver card knows that the disk has
failed a r/w, fails out the disk, runs in degraded mode and
turns on the light. You hotswap the drive (presumably the
failure is visible with software too, but I assume some poor
flunkey patrols the racks once a day with a bucket of
replacement disks). However with software raid, there won't
o What does a disk failure (eg click of death) look like on
s/w raid? If a disk gets a r/w fail does mdadm know about it
straight away? Do you check the output of mdadm every 5 mins
with Nagios/rrdtool type scripts and send messages to
someone to change the disk?
o with s/w raid, if you get a notice that /dev/sdm1 has
failed, how do you find drive /dev/sdm in a rack if there's
no light to turn on? Do you have to label all your drive
bays at install time?
o can you run
smartctl -t long /dev/sdm
on each of the RAID devices? (I assume multipath complicates
things here. Do you test each branch of the multipath
o s/w raid requires intervention at the keyboard to remove
the old drive from mdadm, go to the racks to hotswap the
drive, return to the keyboard, add the new drive, and check
that the rebuild suceeds. If you have 100s of racks, I
assume this process doesn't scale. So wouldn't everyone be
running hardware RAID?
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
jmack (at) wm7d (dot) net - azimuthal equidistant map
generator at http://www.wm7d.net/azproj.shtml
Homepage http://www.austintek.com/ It's GNU/Linux!
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