raid_strategies

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Subject: Re: Software RAID
From: Eric Sisler <esisler@westminster.lib.co.us>
Date: Mon, 25 Oct 1999 10:42:32 -0600


Kevin Diffily <kdiffily@webpageweaver.com> wrote:

>I am trying to set up Software Raid on a 6.0 (soon to be 6.1) system 
>and have read a lot of the how to documents.  I am still undecided as 
>to the best way to proceed and am wondering if anyone would be 
>willing to share their experiences with this.
>
>I would prefer to set up a Single Raid 0 Array and mount it as the 
>Root Device (optimal) or a /boot device and the rest of the 
>filesystem on a RAID Array.

I'm wondering why you want a single RAID 0 array, unless you have several
small disks you want to concatenate into one.  RAID 0 gives you no
redundancy whatsoever, it's just a way to have several small disks appear
as one larger one.

>The docs seem to indicate that mounting 
>the root filesystem is a tricky thing to pull off.

I came to that conclusion as well and decided to go a bit simpler.  While I
will be mirroring my user data disk with RAID 1 after I upgrade to RH 6.1,
I decided against making the boot disk RAID for now.  What I'm doing
currently is using rsync to create a "cold" copy of the boot disk.  rsync
is great for this as it only copies changed files and keeps
owner/group/permissions, etc.  I have it scheduled to run from cron every 6
hours.  In the event of a boot disk failure, I shut the box down, swap the
primary/secondary boot disks and power the server back on.  (I have easily
accessable drives in the server.)  Because of the way I have my filesystems
configured, data on the boot disk doesn't change much and worse case I'd be
missing 6 hours of data.  (Mostly logfiles.)

>I also am unsure 
>how to convert my single disk to a dual disk array without losing all 
>of the data.  It seems as if I would need another drive to manipulate 
>the Raid commands from and to copy the original data to while setting 
>up the array.

I'm not sure there is one.  You'd either need to move the data to another
disk or tape drive and move it back when you're done.  Another reason I
chose not to make the boot disk RAID.  It's easy enough to backup user data
to tape, wipe the drive(s), create the RAID array and restore from tape,
but a little tricker to do so with the boot disk.

===


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