- June 26, 2019 at 1:48 pm
I’m a bit new to LTO solutions and am struggling to find what’s wrong with our setup. We have a mLogic mTape LTO 8 Thunderbolt 3 and are using LTO7 tapes formatted as M8. The maximum transfer speed we are getting with this setup is 30MB per second. All the documentation I’ve read says we should be able to achieve the standard 300MB per second but that’s just not happening. We’re using YoYotta LTFS and are not spanning tapes but treating each as a single “drive” although we are using the Collection and Project catalog within YoYotta.
We have the mTape device connected to an iMac via TB2 to TB3 adapter and the media being backed up is on network storage accessed via 1GB ethernet. We’re backing up a variety of source material, mostly video, in a range of codecs. Some tapes only fit less than 100 ProRes files and others have over 100k mp4s. Neither backup has broken the 30MB per second barrier to my knowledge. Compression is on, YoYotta stated it’s hardware compression and doesn’t slow down the backup even though video will not benefit from it, there may be other files in the archives that would.
When the tapes are verified, this process appears to happen at a “normal” speed because the hours remaining will go from 60+ to 0 in less than a day.
We’re running YoYotta V3 (89) on Sierra 10.12.6. Let me know if I’ve left out any crucial information. Would appreciate any suggestions, best practices, etc… that may correct me of any errors.
- June 26, 2019 at 2:35 pm
To write at full speed to an LTO-7 tape your source will need to supply at least 300MB/s. So your limitation will be the 1Gb network speed.
As a test try archiving a few hundred GB of files from a local SSD or direct attached RAID to tape and see what speed you get.
Can you get a 10Gb link to your shared storage?
- June 26, 2019 at 2:43 pm
Thanks for your quick reply. Once the current tape is done transferring later today I will try a small backup from the internal HD. Since 1gb is 125MB per second it seems to me that there is still another cause of the slowness as we’re not getting even 25% of that.
I also now realize that since we were able to get the TB3 to TB2 adapter working I can test it on my 10gb connection too. I’ll report back with my findings.
- June 26, 2019 at 3:29 pm
LTO-7 drives will attempt to speed match to the incoming data rate, however they need at least 100MB/s to write continuously. Below this speed they will have to stop, rewind and start again, you will hear this “shoe shining” behaviour if you listen to the drive. When this happens your average speed will drop drastically.
A 1Gb network will provide ~ 90MB/s assuming a fast enough source, reasonably sized files and no contention with other storage users. This will not be enough to keep the tape moving.
A figure of 125Mb/s is a theoretical 1Gb network speed using test data and jumbo packets.
If testing with an internal drive ensure it is an SSD rather than an HDD.
The fact that your verification is running normally suggests that there are no other issues.
- June 27, 2019 at 1:25 pm
I was able to test off a raid and get sustained speeds in the 200-300MBPS range so your advise is indeed correct. 1Gb simply isn’t enough bandwidth to keep the tape spinning. I’m working on getting a 10Gb pipe into the machine or possibly moving the iMac to another office where there is already 10Gb networking.
Thanks for all your help,
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