Backing up to tape
Olivier.Nicole at cs.ait.ac.th
Thu Apr 26 10:40:46 UTC 2018
"Frank Leonhardt (m)" <frank2 at fjl.co.uk> writes:
> On 25 April 2018 19:10:02 BST, Sergey Matveev <stargrave at stargrave.org> wrote:
>>*** Frank Leonhardt [2018-04-25 21:00]:
>>>If I plug a SAS drive in to an HBA it'll just appear as /dev/sa0 (or
>>>Then I can backup everything with tar -cf /dev/sa0 /* - right?
>>>Is anyone using tape able to confirm any of this one way or another?
>>I have purchased Ultrium LTO5 SAS tape drive for several months ago and
>>use it with HardenedBSD. Everything you wrote is right. It appears
>>(connected through SAS HBA) as /dev/sa0, /dev/nsa0, /dev/esa0 and you
>>can directly use tar with it without any problems. mt command allows
>>to rewind and seek records on the tape. And neither native tar supports
>>multivolume archives nor tape drive will do anything with it -- you
>>to split volumes manually somehow. You can easily do something like:
>>zfs send zroot > /dev/sa0 to write your ZFS dataset directly to the
>>and then restore from it.
> Thanks Sergey! Good to know the tape stuff still works. I've ordered a drive.
> I'll need a utility to save/restore ZFS datasets that are larger than one tape if anyone knows of one. Otherwise I'll be writing one, if anyone is interested.
While it should not be too difficult to design such a utility, you have
to consider that each time you will want to access any data on the tar,
you will have to stream through all the tapes, because tar format does
not allow you to start with the tape 5 even if you know that the file
you are looking for is not on the first 4 tapes.
And tar will continue to stream through all the trailing tapes even if
the file you are looking for was found on the first tape (I think that
tar strores the newer version of a file at the end of the archive, so it
has to process the tar file to the end to be sure there is no newer
version of the file you extract).
It would be much better to split the data you want to tar, to have one
set of data filling almost one tape.
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