Re: Need suggestions for a USB external hard disk
- From: Douglas Mayne <doug@xxxxxxxxxxxxxxxxx>
- Date: Wed, 18 Jan 2006 13:11:03 -0700
On Wed, 18 Jan 2006 10:41:42 -0700, ray wrote:
> On Wed, 18 Jan 2006 11:04:00 -0500, Madhusudan Singh wrote:
>
>> Hi
>>
>> I am thinking of purchasing an external USB hard disk drive for our OpenAFS
>> (Debian Sarge) server to do vos dumps onto.
>>
>> The current space requirements are about 22G, but could easily grow quite a
>> lot in the future (this being an AFS cell and all). So, I am thinking of a
>> factor of about 10x, i.e., about 200G.
<snip>
>
> My first reaction: get the cheapest one you can find. Linux operability is
> not going to be an issue. I realize that longevity or reliability could
> be, but you basically 'pays yer money and takes yer chances'.
>
I'll second this advice. I have had good luck with USB 2.0 drives
from Western Digital. Recently, the Seagate drives were on rebate,
so I'll give them a try, too.
I don't know what OpenAFS is, so I can't comment on the specifics.
Below, I explain how I use these drives for general backups. You will
need to decide if a similar approach would work for you. This is nothing
fancy- it won't capture open files or databases. It will simply save a
snapshot to your external disc. The snapshot must have already
been acquired by some other means.
1. An external drive is selected for today's backup from the drawer.
These drives are cheap enough that more than one drive can be assigned
to a given job. More drives give more insurance against any type of
drive failure.
1.A. Safety feature: When these drives are not being used, they are
turned off and stored in a drawer.
1.B. Safety feature: When these drives are being transported to a job,
they are kept in a padded box.
1.C Safetey feature: cryptoloop (kernel module)
2. The selected drive is physically connected on the same network with
the data for today's backup, then it is mounted.
3. rsync is used to mirror the important data which is being saved.
Note: in the example below, you should fixup variables to be
appropriate for your system.
CAUTION: This method uses rsync, a command that can do great damage if
used improperly. Experiment with directories where you can limit the
damage until you have it down pat. It is picky about trailing slashes and
dots on pathnames, so make sure you are clear about your intended source
and destination before starting rsync. Obviously, the --delete option can
be dangerous.
DEST=/mnt/sda1/job
B_SRV=backup.server
SOURCE_DIR=snapshots/2006/After_2006-01-06
(cd $DEST && rsync -lptrv --progress ${B_SRV}:${SOURCE_DIR} .)
3.A. I use a network transport because the backup server lacks a USB 2.0
interface. If the USB drive can be connected directly, then see 3.B.
3.B. If the USB drive is connected directly to the backup
server, then no network transport will be necessary. rsync can still be
used by simply omitting the colon. Be clear about specifying your
directory names (absolute or relative paths).
4. The drive is unmounted and returned to the storage drawer.
Here is one more note about performance. I think USB 2.0 in combination
with gigabit ethernet speeds up this operation. The example above works
quick enough for me, even with the added overhead due to encryption (ssh.)
I don't have the fastest computers, but I am able to save data to the disc
at between 5 and 6 MB/s. I guess rsh could be used to omit encryption,
but that raises some security questions. Also, I may _actually_ be
running into the upper limit imposed by the hard disc write operation
(that is, its sustained data transfer when writing.)
--
Douglas Mayne
.
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