Dual HD + RAID --- an interesting challenge
- From: Carlos Moreno <cm_news@xxxxxxxxxxxxxx>
- Date: Wed, 12 Sep 2007 08:11:30 -0700
I'm hoping the gurus and quasi-gurus out there will be able to help me
with this challenge.
The short story first:
I have a machine (Fedora Core 6) that has two hard drives, and they're
configured in RAID-1
(the two hard drives have an identical partition layout, and they're
all paired into md? devices
that are then mounted to / , /home, and /var)
I don't have physical access to that machine, but we do have full root
access through SSH
(it's a dedicated server we're renting).
The challenge: Is there a way for me to configure that machine to
*NOT* use RAID-1, and
instead use the two hard disks independently??
I'm thinking adjusting the fstab file so that it temporarily doesn't
mount things the way it
does, then use mdadm in the /etc/rc.local (or some other earlier
script?) to disassemble the
RAID devices, then mount the partitions at will?
Can this work? I'm not clear on how the RAID configuration is
handled at boot time. How
does the system, after a reboot, still knows that the devices are
RAID-1? (is here something
physically present in the partitions that makes them automatically be
seen as RAID?)
Keep in mind that I can not simply throw an installation DVD and start
over, configuring
the system without RAID.
The slightly longer story:
I'm trying to do this as a "get around" the web hosters' (1&1) lack of
flexibility in terms of
customizing the hardware --- they don't offer us the possibility to
customize the hardware
and put an additional hard drive. (but they're otherwise good hosters
and we don't want
to switch at this time)
The application we're running is PostgreSQL, and we use lots of
transactions to write to
the database --- this is a known "bottleneck" in PG, and the typical
suggested solution to
attenuate the problem is to mount the pg_xlog (the Write-Ahead Logs)
to a partition on a
separate drive that allows truly simultaneous access (as in "hardware
simultaneous").
Since the HD are SATA, they're obviously accesible simultaneously (as
opposed to, for
instance, two IDEs connected to the same channel as primary and
secondary). By avoiding
the RAID-1, I end up with two independent disks, and I can achieve
that configuration
(we do daily backups of the critical data, so sacrificing the RAID-1
redundancy shouldn't
be a critical detail).
Thanks for any help!
Carlos
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