[PLUG] Re: Linux (Debian) and raid

[JP Vossen <jp@jpsdomain.org>]

> Date: Thu, 24 May 2007 22:29:28 -0400 (EDT)
> From: Doug Crompton <doug@crompton.com>
> Subject: [PLUG] Linux (Debian) and raid

<snip>

> How do you bring a virgin system up on raid? Do you first install to one
> drive and then later on create a raid array? With Windows there is a
> driver and you create a raid array and load the OS. Quite easy actually.

Linux is the same, both the Debian Etch and CentOS-5 (RHEL-5) installers 
can do this at OS install time for software RAID, and for hardware RAID 
if the driver is present (I don't know about the Intel device you cite).

There is one point I haven't seen anyone else mentioned yet.  LVM2 is a 
*wonderful* thing.  It may seem complicated, but I have found it to be 
"set it and forget it" once installed.  It allows all kinds of 
flexibility for mixing and matching (and expanding) the underlying 
physical storage device(s).  The LVM-HOWTO [1] is a great intro to most 
of LVM, but it skimps on details (like the following) for snapshots.

LVM2 also allows volume point-in-time snapshots, which can be great for 
backups.  BUT, the installers max out the Logical Volume (LV) size and 
fill up the Physical Volume (PV) resulting in a "Insufficient free 
extents in volume group" error if you try to create a snapshot.  So when 
setting up the system, you have to deliberately leave free space in the 
PV or else you can't use snapshots.  I'm not 100% sure how to do that in 
the installers (haven't tried yet), though I think you can just manually 
make the LV size smaller than "max".  Worst case you can resize the 
volumes after install if necessary [2].

Good luck,
JP

[1] http://www.linux.org/docs/ldp/howto/LVM-HOWTO/index.html

[2] See my small write-up on this topic at 
http://www.backupcentral.com/components/com_mambowiki/index.php/Backup_%26_Recovery:_Ch.22_MySQL_Backup_%26_Recovery.
----------------------------|:::======|-------------------------------
JP Vossen, CISSP            |:::======|        jp{at}jpsdomain{dot}org
My Account, My Opinions     |=========|      http://www.jpsdomain.org/
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