Very Slow Tape Performance

M

ManFriday

New Member
Proxmox Subscriber
Mar 20, 2024
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Hi all,

I’m experiencing extremely slow tape backup performance using Proxmox Backup Server (PBS), and I’m trying to determine the bottleneck. My backups are writing to LTO8 tapes at speeds as low as 18MB/s, occasionally peaking at 45MB/s, which is far below what LTO8 and my infrastructure should be capable of.


Hardware Setup


• Backup Storage Repo:


• Hitachi array (Nearline 7200RPM, RAID 6)


• Served to PBS via a pair of 8GB Fibre Channel (FC) links


• 4 paths (Round Robin) configured


• Tape Library: Spectra Logic T950


• Drive 1: IBM LTO8 (Dedicated 8GB FC uplink)


• Drive 2: IBM LTO8 (Dedicated 8GB FC uplink)


• Tape FC connections are separate from storage FC connections


Performance Issues

• Tape write speeds fluctuate between 18MB/s and 45MB/s to a single drive


• Well below expected performance for LTO8 and FC


ATOP Analysis:


• Storage utilization is hitting 99%, despite the storage admin stating the array is not under stress


• High disk wait times (average I/O wait at 86%)


• High LVM device utilization (92%) on the backup repo


Comparison to Veeam:


• This same storage was previously used with Veeam, and we did not have tape performance issues


• I suspect this may be because Veeam utilizes multi-threaded writes, whereas PBS seems single-threaded?



Questions:
1. Is it possible to increase the number of backup streams or tune PBS settings to improve performance?


2. Has anyone optimized PBS for high-performance tape backups using similar storage?





Any insights or similar experiences would be greatly appreciated!
 
It looks like this issue has been discussed before:

Low ZFS Read Performance (Disk → Tape)

Has there been any progress on enabling multithreaded tape backups in PBS? From the previous discussion, I see concerns about potential server overload, but would it be possible to implement an optional setting where users can specify the number of threads?

This seems to be how Veeam handles tape backups, and it could significantly improve performance for those with capable hardware.

Right now, the disk-to-tape performance in PBS is a showstopper for us, and we’re struggling to find a way to improve it. Has anyone found workarounds, or is there any development planned in this area?
 
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