[geeks] Linux tape backup help

[Mark Benson]

Firstly thanks for everyone's input. This is learning by practical
application, and I'd like to at least try and get it right :)

So far I have the stinit.def setup pinned down for the drive, Quantum
helpfully printed that in the Appendices of the Linux Guide for the drive.
Damned useful of them!

The drive responds to a stinit command now correctly so tomorrow will be
'attack it with a tape and see what happens' day. I have a 'spare' tape that
was a freebie with the drive I can use as a scratch for testing.

On 14 Jan 2010, at 18:56, Patrick Finnegan wrote:

> On Thursday 14 January 2010, der Mouse wrote:
>>> The server is essentially a Ubuntu LAMP environment with samba and
>>> dns facility added.  The mainstay of the backup will be [...]
>>
>> If you have enough disk space, I'd echo a suggestion someone else
>> made of backing up to a disk file first, so you have the actual
>> backup size before you start writing to tape.

At the present time I'm not short of hard disk space. I can easily tarball ->
get filesize -> check -> write to tape for now. Sounds like a good plan. If it
gets to a point of not fitting the array disks I can always add another 500GB
disk to the server and use that instead.

> I'll second this, but I'm not sure that adding another machine into the
> mix will be advisable.  You really want to try to keep the drive writing
> at full speed, which requires 60MB/sec for a 1/2ht drive or 80MB/sec for
> a full-height drive, which means that you'll need to read the backup off
> of some sort of RAID.

The main storage is a RAID1 mirror and it is pretty fast. I think it'd easy
keep up the speed required for the tape drive - it's 1/2 height SCSI drive
hanging off an LSI U320 card. We have no budget for a backup machine and
moreover have no machines suitable onsite that would take the LSI card in
order to run the tape drive.

> Also, the "wear" on the tape from not writing a full tape is not what
> you may think it is.  For LTO-3, the drive makes 44 passes end-to-end to
> write one tape.  So, the tape will move completely across the tape head
> once for every ~9GB (uncompressed) of data that you write to the tape.

Is there any difference between tape pass wear or write-to-tape wear? I'm only
accustomed to disk or SSD storage issues of sector drop from tired/worn
material. Tape doesn't work the same I guess - I guess the many parallel
tracks are designed with the purpose of spreading tape wear out over the whole
tape, as well as allowing parallel access to a larger data area?

> There's a lot of useful information on the wikipedia page on LTO:
> http://en.wikipedia.org/wiki/Linear_Tape-Open

Thanks, sometimes the blatantly obvious fails me while looking for the obscure
:D I look up stuff about space suits, rocket engines and bands on Wikipedia
and forget there's a ton of info about computer stuff on there ;)

--
Mark Benson

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