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dan wrote:
> The thing is that it isn't possible to have a perfectly synced remote
> copy of a filesystem at every single moment unless they are tied
> together in something like raid1 and all writes are syncronos, which
> would be murder on performance. Otherwise, there will always be a delay
> for the remote sync. at least with a clustered filesystem, the remote
> write is immediately queued up so the maximum delay between local or
> remote syncing is dicated by the bandwidth between them and not by a set
> time and a cron script.
You might also take a look at nbd which can achieve the same sort of
thing.... ie, using a RAID1 with one local and one remote member...
Personally, I use this (not on backuppc but on a file server) with a
RAID5 local member and a remote member which is itself a RAID5 device on
the remote machine. Thus I can lose one whole machine, plus one drive,
and still not suffer downtime/loss of data. Of course, these days RAID6
might be better, but you can only fit so many disks in a box :(
> Alternatively, you could try to raid1 over a remote iSCSI and rely on
> the device mapper to handle the syncing on the block level. You could
> also use a compressed ssh tunnel to pipe the iSCSI packets between sites
> but you should probably put that tunnel in xinet so it is initiated each
> time it is needed or reinitiated when it is dropped.
>
> The issue with that is that a de-sync of the mirror would cause a
> rebuild of the mirror set, which would probably sync the entire drive
> which would take ages!
AFAIK, nbd can solve this problem... though I've not used it extensively
since in my case they are both on the same gigabit LAN...
BTW, I am not certain that nbd (or any other solution) is the
ideal/perfect solution for this or any other problem. They are many way
to solve each problem, I just thought I'd add another possible solution.
AoE looks interesting, but is restricted to local LAN, I think nbd works
over TCP/IP, and of course can be tunnelled over your VPN or ssh tunnel,
etc...
Regards,
Adam
- --
Adam Goryachev
Website Managers
www.websitemanagers.com.au
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