Tape backup is very slow

[TheNetStriker]

I just tried the tape backup of the Proxmox Backup server, but the transfer speed is very slow. (Max 60 MB/s)

I also use the same tape with Bareos and there I found out that setting the tape block size to 1 MB made a sigificant performance improvment. (From under 100 MB/s to over 300 MB/s)

Is it possible to increase the block size of the tape backup in Proxmox Backup Server?

 

[dcsapak]

hi,

Is it possible to increase the block size of the tape backup in Proxmox Backup Server?

no we use a blocksize of 256k and this is currently not configurable

but we generally are able to hit maximum tape speeds if the source storage is fast enough

what kind of source storage do you use? (e.g. hdds? ssds? some kind of raid?)

(also we recently fixed one performance bug that is not yet packaged, and one patch is still pending review that would allow a performance increase for certain storage types)

 

[TheNetStriker]

The Proxmox Backup server runs as a virtual machine on my TrueNAS with 8 HDD's in a vdev. I know this is not officially supported, but I don't want to run an additional machine just for the backup to save energy. With a dd write speed test on the backup volume I get 679 MB/s.

Bareos runs on the same machine and is also backing up data from the same machine and there I have much higher transfer speed. So I guess it should not be a problem that the storage is too slow.

 

[dcsapak]

well the current code only reads from the filesystem in with one thread and the data we read consists of many small files, so the comparison with dd is sadly not really applicable
the patch currently in review is an option to increase the number of parallel threads used to read from the storage, which can have a large impact on such raid arrays, see e.g. here: https://forum.proxmox.com/threads/low-zfs-read-performance-disk-tape.139494/

bigger blocksize wouldn't make much difference here when the bottleneck is reading from the storage

i don't know the inner workings of bareos, so i can't comment on that comparison really, just know that we use the pbs tape backup ourselves and we usually get nearly drive performance when using fast storage (e.g. sata ssds or nvmes)