building a RAID system - 8 drives

Jeff Layton jeffrey.b.layton at lmco.com
Thu Oct 9 07:02:57 EDT 2003


Alvin Oga wrote:

>
> On Thu, 9 Oct 2003, Jeff Layton wrote:
>
> > > > How do you stick 2TB in a 1 U server?  I've seen 1U cases with four
> > > IDE bays,
> > > > and the largest IDE drive I've seen is 250 GB.
> > >
> > > 8 drives ... 250GB or 300GB each ..
> > >
> >
> >    Cool. Do you have pictures? How do you get the other 4 drives
> > out? I assume they're not accessible from the front so do you
> > have to pull the unit out, pop the cover and replace the drive?
>
> yup.. pull the cover off and pop out the drive the hard way vs
> "hot swap ide tray"
>
>         autocad generated *.jpg file
>         http://linux-1u.net/Dwg/jpg.sm/c2500.jpg
>
>         ( newer version has the mb and ps swapped for better cpu cooling)
>         http://linux-1u.net/Dwg/jpg.sm/c2610.jpg ( also holds 8 drives )
>
> > > i/we claim that if the drives fail, something is wrong ... its not
> > > necessary for the disks to be removable
> > >
> >
> >    Are you saying that it's not necessary to have hot-swappable
> > drives? (I'm just trying to undertand your point).
>
> if the drive is dying ....
>         - find out which brand/model# it is and avoid it
>         - find out if others are having similar problems
>         - put a 40x40x20mm fan on the (7200rpm) disks and see if it helps
>
> i'm not convinced that hotswap ide works w/o special ide controllers
>         - pull the ide disk out while its powered up
>         - pull the ide disk out while you're writing a 2GB file to it
>
>         - or insert the disk while the rest of the systme is up and
>         running
>
> if you have to power down to take the ide disk out, you might as
> well do a clean shutdown  and replace the disk the hard way with
> a screw driver instead of nice ($50 expensive) drive bay handle
>         $ 50 can be an extra 80GB of disk space when a good sale
>         is occuring at the local fries stores 
>

   We've got several NAS boxes with hot-swappable IDE drives
and without it we'd be toast. Granted the controller is specialized,
coming from one vendor, but it allows us to have a fail-over
drive with auto-rebuild in the background. Then we just pull
the bad drive, put in a new one, and designate it as the new hot
spare. Works great! It's saved our bacon a few times. I've
wanted to test hot-swap with 3ware controllers, but have
never done it. Has anyone tested the hotswap capability of
the 3ware controllers/cases?
   Another comment. If you have to pull the node to replace
the drive, then you have to bring down the filesystem which
might not be the best thing to do. Hot-swapping allows the
filesystem to keep functioning, albeit at a lower performance
level.

> >    Does everyone remember this:
> >
> > http://www.tomshardware.com/storage/20030425/index.html
> >
> > My only problem with this approach is off-site storage of
> > backups. Do you pull a huge number of drives and move them
> > off-site? (I still love the idea of using inexpensive drives for
> > backup instead of tape though).
>
> i suppose you can do "incremental" backups across the wire ...
> and "inode" based backups too ...
>
>         - it'd be crazy to xfer the entire 1MB file if
>         only 1 line changed in it
>

   We can't do backups across the wire to an offsite storage
facility. So we have to do backups, pull the tapes, and store
them off-site. I'm just not sure how this would work with
disks instead of tapes. Oh, you can full and incremental backups
to disk - most backup software doesn't care what the media
is anyway - but I'm just not sure if you pull a set of disks
and store them. How does off-site backup recovery work?
Do you pop them in, mount them as read-only, and copy them
to a live filesystem? However, despite all of these questions,
at some point soon, disk will be the only way to get backups
of LARGE filesystems in a reasonable amount of time.

Jeff

-- 
Dr. Jeff Layton
Chart Monkey - Aerodynamics and CFD
Lockheed-Martin Aeronautical Company - Marietta


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