[ale] RAID1 h/w suggestions

[Greg Freemyer]

n 7/9/05, Jim Popovitch <jimpop at yahoo.com> wrote:
> This really has more to do with WinXP than Linux, but the focus should
> be more on hardware than OSes or software.... ;-)
> 
> I need a highly robust hardware solution for a system currently running
> WinXP.  What I want is the ability to have a RAID1 (mirror) array across
> 2 disc drives (one internal, one external) where the external drive is
> replaced and moved to off-site storage every few days.  I would like to
> not have to bring the system down to do this, and would prefer if the
> hardware (or even WinXP) allowed for the insertion/extraction of discs
> and the auto-rebuilding of the array.
> 
> Questions:
> 
>    Years ago this was SCSI only type functionality, does anyone
>       know if SATA or EIDE can natively support hotswapping?
> 
>    Does WinXP Pro support software RAID1, and will that work in
>       this case, if the underlying hardware supports hotswapping?
> 
>    Hardware suggestions?
> 
>    Alternate suggestions?
> 
> 
> Short explanation:
> 
>    This system is used for studio content development work (MIDI,
>      etc) and produces lots of really large WAV/MIDI files that
>      need short-term security and preservation.
> 
> Thanks,
> 
> -Jim P.
> 
> _______________________________________________
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> Ale at ale.org
> http://www.ale.org/mailman/listinfo/ale
> 

I think your asking too much of XP to do that reliably.  With Win2003
you might be able to do what you want reliably.

_if_ you were working with Linux (and you had only my knowledge base
to work with), the below is what I would do:

1) Use a 3ware PATA or SATA RAID controller and setup a RAID1 with one
or both of the drives being removable.  (3ware supports "cold-swap"
with both PATA and SATA.  Cold-swap is like hot-swap except you have
to tell the controller what is happening, not just physically
disconnect and reconnect your drives. (ie. no auto-rebuilds)).

1a) Disable write-cache on the 3ware controller and on the individual
drives.  Having data only in cache will kill you when you pull the
drive.

2) Put a XFS filesystem on the RAID set.

3) When you want to pull a backup, issue a "xfs_freeze -f" command to
tell XFS to put a stable filesystem on disk and then to stop doing any
i/o to the underlying disk.

4) Pull the drive.  (I don't know a programatic way to break the
mirror with 3ware.)  (I use ICY Dock PATA bays specifically designed
to do this.  The 3ware cards specifically support pulling the drive in
this way without damaging the drive/controller.)

5) Issue a "xfs_freeze -u" to release XFS and allow it do i/o's again.

6) Verify/Ensure, via the 3ware CLI/GUI, that the missing drive is
marked failed.  (you may need to read/write something to the
filesystem if there is no normal activity.  The 3ware card will not
miss the drive until it tries to read/write to it.)

7) Put in a replacement drive.  From the 3ware CLI/GUI start a rebuild.

I'm sure there are other raid controllers that would work and other
filesystems that support the freeze option, but I have experience with
everything above and am pretty confident it would work.  (Actually
I've only used the 3ware PATA controllers, but I've heard good things
about the SATA controllers too.)

I do not think XP supports a function like xfs_freeze.  Without that
you have no way of knowing it the pulled drive will have a good
filesystem image on it or not.  i.e. When you plug that drive into
your restore environment, the very files you want to backup may not be
available because a chkdsk will find them inconsistent and delete
them.

I don't know if Win2003 supports this type of functionality or not,
but I suspect it does.  The xfs_freeze functionality is most commonly
used in a SAN environment and Win2003 has a lot of SAN support from
what I understand.

HTH
Greg
-- 
Greg Freemyer
The Norcross Group
Forensics for the 21st Century