External USB hard drive

Harold Weissman · External Since: Jan 24, 2007 Posts: 31

I wonder if people who have used such hardware under Linux could
contribute their experiences? I am interested in performance and
reliability, mostly, but also on setup simplicity. In particular, would
using such a hard drive be an appropriate medium for backups? I would be
interested for the drive to be active only when the backup is being
performed; I understand that these drives can be configured so that they
stop spinning after they have not been accessed for some time.

Anton Ertl · External Since: May 21, 2006 Posts: 169

Harold Weissman <HaroldW22 RemoveThis @hotmail.com> writes:
> I wonder if people who have used such hardware under Linux could
>contribute their experiences? I am interested in performance

The transfer rate is limited to about 30MB/s (if you get a fast
USB/IDE interface, there are also slower ones around), otherwise the
performance is the same as for internal drives.

>reliability,

No problems in my experience.

> mostly, but also on setup simplicity.

They are very simple to set up. Plug them in, turn them on, mount
them (or you can automount them through hotplug or on-demand). Oh,
partition and format them the first time.

> In particular, would
>using such a hard drive be an appropriate medium for backups?

Yes. I am using them for this purpose.

> I would be
>interested for the drive to be active only when the backup is being
>performed; I understand that these drives can be configured so that they
>stop spinning after they have not been accessed for some time.

IDE drives can be configured to do that, but IME they are configured
by default not to spin down, and you cannot tell them to spin down
with "hdparm -S ..." through the USB interface.

However, if you want to use them as a backup medium, I would recommend
to remove them anyway while not backing up, for several reasons:

- You should store the backups as far away from the main storage as
practical, for increase safety against localized disasters (e.g.,
fire, theft).

- You don't want all the backup disks to be on-line when a cracker
breaks in and trashes all the hard disks he can reach.

- anton
--
M. Anton Ertl Some things have to be seen to be believed
anton RemoveThis @mips.complang.tuwien.ac.at Most things have to be believed to be seen
http://www.complang.tuwien.ac.at/anton/home.html

Chris · External Since: May 27, 2005 Posts: 473

Harold Weissman wrote:
> I wonder if people who have used such hardware under Linux could
> contribute their experiences? I am interested in performance and

I have recently acquired a Western Digital MyBook 250GB and the
performance is very good on a USB2 interface.

> reliability, mostly, but also on setup simplicity.

I haven't had a chance to test the reliability as it's still new, but
setup was simply a case of plugging it in and Mepis automounted it.

> In particular, would
> using such a hard drive be an appropriate medium for backups?

That's what I'm using mine for.

> I would be
> interested for the drive to be active only when the backup is being
> performed; I understand that these drives can be configured so that they
> stop spinning after they have not been accessed for some time.

The MyBook automatically spins down after a certain amount of inactivity
and will switch itself 'off' when unmounted.

Scott Alfter · External Since: Sep 18, 2006 Posts: 27

In article <2007Jul30.205026.RemoveThis@mips.complang.tuwien.ac.at>,
Anton Ertl <anton.RemoveThis@mips.complang.tuwien.ac.at> wrote:
>Harold Weissman <HaroldW22.RemoveThis@hotmail.com> writes:
>> I would be
>>interested for the drive to be active only when the backup is being
>>performed; I understand that these drives can be configured so that they
>>stop spinning after they have not been accessed for some time.
>
>IDE drives can be configured to do that, but IME they are configured
>by default not to spin down, and you cannot tell them to spin down
>with "hdparm -S ..." through the USB interface.

sg3_utils includes a command, sg_start, that'll manually spin down USB hard
drives. If you wrap it in a shell script that runs every few minutes as a
cron job, it'll spin down your drive when it's not in use:

#!/bin/sh

# needs sg3_utils 1.23 or later

source /etc/profile

if [ \! "`fuser -c /mnt/music 2>/dev/null`" ]
then
sg_start --stop /dev/disk/by-label/music
fi

if [ \! "`fuser -c /mnt/video 2>/dev/null`" ]
then
sg_start --stop /dev/disk/by-label/video0
fi

This particular script spins down the two drives hanging off my MythTV box
for music & movie storage. For each drive, it first checks the mount point
for open files on the drive. If there are no open files, the drive is told
to spin down. Any activity on the drive that can't be handled by the cache
will cause the drive to spin back up. I have this script set to run every
10 minutes.

_/_
/ v \ Scott Alfter (remove the obvious to send mail)
(IIGS( http://alfter.us/ Top-posting!
\_^_/ rm -rf /bin/laden >What's the most annoying thing on Usenet?

Hendric Stattmann · External Since: Dec 25, 2006 Posts: 29

Harold Weissman wrote:

> In particular, would
> using such a hard drive be an appropriate medium for backups?

Hello Harold,

In addition to the other replies, I would like to recommend you the tool
named "StoreBackup". This utility does make daily backups of selected
folders to a ext3 (or similar, but not FAT or NTFS) partition. Instead of
copying the whole lot of files and eating up your disk space in no time, it
uses hard links for unchanged files and actually copies only the
new/changed ones. Thus, you have available complete daily snapshots of your
data, by simply using any file browser.

StoreBackup Homepage: http://sourceforge.net/projects/storebackup
Tutorial specific to SuSE: http://en.opensuse.org/StoreBackup

With regards,
Hendric
--
> Hendric Stattmann, Mödling, Austria. Registered Linux User #178879

ray · External Since: Nov 13, 2004 Posts: 3312

On Mon, 30 Jul 2007 15:58:54 +0000, Harold Weissman wrote:

> I wonder if people who have used such hardware under Linux could
> contribute their experiences? I am interested in performance and
> reliability, mostly, but also on setup simplicity. In particular, would
> using such a hard drive be an appropriate medium for backups? I would be
> interested for the drive to be active only when the backup is being
> performed; I understand that these drives can be configured so that they
> stop spinning after they have not been accessed for some time.

I've used a USB external for backing up partitions on my laptop when I
swapped out the 40gb drive for a 120. Also restored after. Works fine.
Firewire will give you faster speeds.

Gregory Shearman · External Since: Jun 30, 2004 Posts: 361

Hendric Stattmann wrote:

> Harold Weissman wrote:
>
>> In particular, would
>> using such a hard drive be an appropriate medium for backups?
>
> Hello Harold,
>
> In addition to the other replies, I would like to recommend you the tool
> named "StoreBackup". This utility does make daily backups of selected
> folders to a ext3 (or similar, but not FAT or NTFS) partition. Instead of
> copying the whole lot of files and eating up your disk space in no time,
> it uses hard links for unchanged files and actually copies only the
> new/changed ones. Thus, you have available complete daily snapshots of
> your data, by simply using any file browser.

Hmmm...

Hard links won't work across filesystems so you cannot put your backups on
another hard disk.

What happens if your disk (or filesystem becomes corrupted? You lose both
your data and your backup.

I use lvm-snapshots and rsync to update my systems onto a separate and
external HDD.

Sorry, didn't look at your link. Maybe there's a way to get around the above
problem.

--
Regards,

Gregory.
Gentoo Linux - Penguin Power

Hendric Stattmann · External Since: Dec 25, 2006 Posts: 29

Gregory Shearman wrote:

> Hard links won't work across filesystems so you cannot put your backups on
> another hard disk.

Hi Greg,

The links are not put between the backup HD and the original files, but only
between files on the backup HD, in order to save space and still make
differential backups look like full backups to the user.

Hendric
--
Hendric Stattmann, Mödling, Austria. Registered Linux User #178879

Gregory Shearman · External Since: Jun 30, 2004 Posts: 361

Hendric Stattmann wrote:

> Gregory Shearman wrote:
>
>> Hard links won't work across filesystems so you cannot put your backups
>> on another hard disk.
>
> Hi Greg,
>
> The links are not put between the backup HD and the original files, but
> only between files on the backup HD, in order to save space and still make
> differential backups look like full backups to the user.

Ah, it all makes sense now.

--
Regards,

Gregory.
Gentoo Linux - Penguin Power

Michael Faurot · External Since: Jan 18, 2007 Posts: 3

Harold Weissman <HaroldW22 DeleteThis @hotmail.com> wrote:
> I wonder if people who have used such hardware under Linux could
> contribute their experiences? I am interested in performance and
> reliability, mostly, but also on setup simplicity.

Performance is good enough.

Reliability can vary. I've run into numerous problems with the
Maxtor external drives. With Maxtor's external USB enclosures , the
drive would overheat the on-board controller and cause the whole
device to drop off the USB bus. The only way to get it back would
be to power cycle the external drive. I got tired of dealing with
this one or more times a week so I wound up pulling the drive out of
Maxtor's external enclosure and just mounting it in the server.
I've also seen this problem with other vendor's external enclosures.
I don't really know of good enclosure to recommend, but I would
suggest that you get one that has plenty of cooling capacity in it
(i.e., fans). I'd avoid any of the enclosures that rely on passive
cooling alone to deal with heat transfer.

Assuming your distribution/kernel are configured for USB storage,
using these devices is pretty simple. Typically plug them into the
USB bus, wait for them to be detected, and then mount using whatever
the device (e.g., /dev/sda1) the drive was detected as. If you're
going to use more than one of these devices, you can run into issues
where one device might be detected as /dev/sda sometimes and maybe
/dev/sdb others. Use labels on your filesystem(s) and then use the
LABEL= syntax within /etc/fstab. With labels, you don't have to worry
about what order the devices get detected and what device name they
get assigned.

> In particular, would using such a hard drive be an appropriate medium
> for backups?

Assuming you get reliable hardware, it works well. I like to use
rsync for the stuff I do.

> I would be interested for the drive to be active only when the backup
> is being performed; I understand that these drives can be configured
> so that they stop spinning after they have not been accessed for some
> time.

Some of these enclosures are "smart", in that they'll spin the drive
down if they detect it hasn't been active in awhile. You can help
facilitate that by only mounting the drive when you're going to do
the back-up. For the backup scripts I've written, I start off by
mounting the drive/filesystem, do an rsync backup, and then umount
the filesystem. This insures there's not going to be any activity
against the filesystem and thus will allow the drive to spin down.
If the enclosure itself doesn't have this feature, there's other
ways to spin the drive down, as others have all ready replied.

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