speedup backup

[mike2012]

Have read alot, but there seems not to be a "one fits it all" solution.

My main backup is on Spinning disks. ( fixed amount that can not be changed )
(4 * 4TB ,16 GB Ram )
Only Proxmox VM's are backed up.
Could attach 2 Sata SSD (each 1TB).

My question is how to use theses 2 SSD

What would give the best effect L2Arc, cache or used as mirrored special device.

And what has the most use of which solution ( speed up Backup, sync,prune, garbage collection )

 

[aaron]

The two SSDs are a bit overkill for a special device as they are quite big. But that would make the most sense.

We did a few benchmarks ourselves with a 7 disk raidz2 pool for the backup storage (7x ST4000NM0033-9ZM170). Without a special device the speed for a verify and garbage collection run were as follows:

verify: 5h 30m 28s
gc: 23m 29.1s

With a special device (INTEL SSDSC2BB120G6) the results were:

verify: 4h 32m 42s
gc: 1m 59.5s

So yeah, certain actions definitely benefit from a special device. You could also configure the dataset where you store the backups to store small files on the special device with the special_small_blocks property.

 

[fabian]

if you do frequent sequences of backups followed by those new backups being synced offsite, a L2ARC might also speed up the syncs (if the recent backup data is still in L2ARC), but you'd have to test that with your work load (and it will cause a lot of churn, so you need SSDs that are up for the task w.r.t. endurance). as @aaron said, special vdevs will likely give you more benefit, an slog almost nothing.