Re: using fsck in a lowmem environment

[Colin Percival <cperciva@tarsnap.com>]

On 11/17/11 12:15, Mark Smith wrote:
> It seems like I can't use --fsck on a small VM. All I really want to
> do is use this machine to manage backups (list them and delete them),

Hmm, that's probably not a good plan.  Tarsnap needs an up to date cache
directory in order to create or delete archives, so if you delete an
archive on said small VM the system which is creating archives won't be
able to create any more backups until its cache directory is brought back
into sync with the Tarsnap server -- i.e., until either it runs fsck or
you copy the cache directory across to it.

> but it seems I can't do that on a small VM -- I have to allocate a lot
> of RAM just to enable it to fsck.

Yes, fsck needs to generate a list of all the blocks you have stored and
how many times each of them is referenced.  Of course, you'd need the
same amount of memory in order to create or delete any archives (since
those will need to update those block reference counts).

> Is there a supported way to use tarsnap on a small machine?

Sure, store less data. ;-)

Aside from that (semi-serious) answer, no.  I think it would be possible
to change how tarsnap does things in order to reduce the memory usage at
the expense of adding considerably more I/O, but I haven't investigated
this in detail and it would likely require significant work -- and most
people have more than enough RAM based on the amount of data they're
storing.

-- 
Colin Percival
Security Officer, FreeBSD | freebsd.org | The power to serve
Founder / author, Tarsnap | tarsnap.com | Online backups for the truly paranoid