[CentOS] Software RAID setup ideas and an apology.
lowen at pari.edu
Sat Sep 10 14:16:51 UTC 2005
The apology first. If I've offended anyone, or just annoyed anyone, I
apologize for that. I sometimes can go 'off the deep end' when I'm being
sarcastic (an old habit from my news.admin days when I ran a Usenet site in
the early 90's), and I'll try to not go into news.admin mode here in the
Now, the question. I have a few ideas about how to do this, but am not sure
of the ideal way of doing it. It has to be a pretty common thing to do, so
I'll ask it here.
I have a server (Dell PE 1600SC) with two SCSI host adapters: a U320 LSI/MPT
for internal drives only, and an Adaptec 39160 with two internal and two
external U160 channels. I have set up a software RAID config with LVM2 on
top (CentOS 4) with four 36GB 15K RPM Ultra 3 drives. The internal drives
are set up with /dev/sda and /dev/sdb partitioned with 100MB /boot (for sda)
and 100MB /boot2 (backup on sdb), and the rest of each drive as mirrors on a
RAID1. /dev/sdc and sdd have each a single RAID partition and are likewise
mirrors in a RAID1. So I have /dev/md0 and /dev/md1, which are then two
parts of a physical volume with the various logical volumes under that. This
works and performs well, all things considered.
Now, the 39160 HBA is attached through one of its two channels to a donated
Cisco Storage Array 12 with 12 18GB drives in it. Unfortunately, the second
channel of the SA12 isn't working properly (it automatically configures split
bus for the array if the second channel is activated), so I'm limited to a
single channel with 12 drives on it. I have the hardware portion of this
working, all drives are recognized, etc both at the Adaptec BIOS level and at
the Linux kernel level (/dev/sde through /dev/sdp).
My question is, what is the opinion of those on the list with experience in
this area as to the 'best' method of joining these drives. I would like to
be able to lose two or more drives and still have redundancy; I had thought
about pairing drives in RAID1's and LVM over the array; and I had thought
about a big RAID5. But I don't want to shoot performance through the foot,
either. I don't have a good hardware RAID controller for this box, so that's
not at this point an option (I have some hardware RAID controllers, but the
ones that work ok with this array have much slower SCSI busses, and the boot
up behavior of this particular array causes the good RAID controllers I do
have with Ultra 3 interfaces to go crazy (the array powers up when it
receives signal from the host adapter: not each drive, but the WHOLE ARRAY
powers up on command; the DPT controllers I have simply refuse to recognize
any drives at all on the bus, regardless of spinup delay (I set it to 60
seconds and still no joy; the 39160 recognizes all the drives just fine))).
Maybe one of those slower controllers might be better than software RAID1; but
at this point I'm open to suggestions.
Director of Information Technology
Pisgah Astronomical Research Institute
1 PARI Drive
Rosman, NC 28772
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