Ermanno Novali wrote:
> Hi everyone,
>
> I'd like to mirror the backuppc pool - I searched through ml archives
> and found that mirroring the backuppc pool (wherever it is) with rsync
> on an external hard drive isn't efficient and doesn't scale good -
> i've tried myself and is cpu and time consuming and very very long for
> big pools - not very reliable.
> In this ml the best solutions for this task are two hdd with pool on
> them (two external, or two in raid maybe) or dd form pool to external
> mirror disk - but NOT mirroring the backup with rsync or something
> like that - right? can you confirm that?
>   
Yes. RAID1 and dd are equally "good" except that to use dd you must stop
backuppc and unmount the filesystem dor the duration of the dd (with
RAID1 you only need to unmount the FS just before you break the RAID to
remove the external drive).
> And dd is time consuming like rsync but more reliable for backuppc pool?
>   
Generally dd and RAID1 will copy the entire pool in the time it takes to
read the entire disk and write the entire disk. The problem with cp and
rsync etc is that they need to read the filesystem structure, and make a
huge number of small reads and small writes. Especially rsync needs to
read the entire list of filenames and store them in memory before even
starting to copy the data to the destination. This is what makes rsync a
poor choice.

Of course, I've not discussed if or how the changes in rsync v3 modify
the above discussion, AFAIK, it is meant to solve or improve the
situation by starting to copy the content before reading the entire file
list, and also being less memory intensive while copying the data.

Also, if your pool is only 10G of data, and your filesystem is 2TB, then
rsync or cp will work better. The above discussion mostly applies to
large pools..... Although the definition of "large pools" is somewhat
murky, and it differs depending on your backuppc hardware, I would guess
something around 500G would be large...

Regards,
Adam

-------------------------------------------------------------------------
This SF.Net email is sponsored by the Moblin Your Move Developer's challenge
Build the coolest Linux based applications with Moblin SDK & win great prizes
Grand prize is a trip for two to an Open Source event anywhere in the world
http://moblin-contest.org/redirect.php?banner_id=100&url=/
_______________________________________________
BackupPC-users mailing list
BackupPC-users AT lists.sourceforge DOT net
List:    https://lists.sourceforge.net/lists/listinfo/backuppc-users
Wiki:    http://backuppc.wiki.sourceforge.net
Project: http://backuppc.sourceforge.net/