I'm having a hard time determining an issue with a new LTO-8 IBM drive/tape.
Hoping someone may have run into this already.
I've used Bacula for around 9 years, most recently with an LTO-6 HH IBM drive without any real issues. I did know that I never was able to reach native speeds but close at around 140MBps with uncompressible data. Since it was close enough, I never really bothered to troubleshoot further.
Recently I've moved to a new LTO-8 drive and I'm finding I'm also not able to reach close to native speed.
I currently max out at 289MBps (exactly) with uncompressible data and ~415Mbps with zeros/highly compressible data.
With ST, the block size is set to variable and changing this makes very little difference (see below for clarification).
I've tried just about everything I can think of short of swapping the SAS cable (SFF-8088 to SFF-8644).
I've tried both Debian 11 with the built-in ST driver on the 5.19.x kernel and itched to CentOS 8 with built-in ST driver on 5.18.x kernel and finally installed IBM's (lin_tape/lin_taped) kernel module. Zero change in speed.
To further troubleshoot and to ensure Bacula wasn't the bottleneck I tested with IBM tape diagnostic tools. The numbers are nearly identical to what the Bacula client daemon reports. ITDT is able to test multiple block sizes and while there is small difference between a 1MB block vs 256kb, I don't believe block size to be an issue here.
I have also tried with two different HBAs (both in HBA/IT mode) one being dedicated Dell 12gb/s (LSI3008 chip) and the other an Adaptec ASR8885. No other data is flowing through the controllers. The firmware is up-to-date on both. The drive firmware is the latest too.
As for the SAS cable itself I'm reluctant to replace it because the one (actually a 2-pack) I'm using was purchased in 2016 from Amazon and the replacements look to be the exact same thing. While I could purchase one through ATTO/Dell/etc I'm concerned that the fact that these have an SFF-8644 end, they should be SAS 2.1/3.0 compliant and support at least 6GB/s.
Has anyone found their SAS cable to not be compliant or have similar issues where a cable swap worked?
Or maybe I'm missing something really simple?
Thanks!
-Drew
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