UFS SMR and UFS/ZFS compatibility

D

dkline201

What is the status of ZFS/UFS and SMR (shingled magnetic recording HDDs)? We use LARGE HDDs as storage - "write once, read many" application where the "host managed rewrites" would not be a killer. The Content drives will be UFS. But I am not seeing good news currently.
 
With device-managed SMR, any file system should work. It might have bad performance, but you might not care. It would be interesting to hear whether any FreeBSD file systems have become device-managed SMR aware, and have changed their layout algorithms to get better performance on SMR.

Host-managed SMR will require changes to the IO stack (file system, block device layer). I do not know the status of any such changes in free file systems, but would be interested to hear about them.
 
Thanks for your prompt reply. We are evaluating 8, 10, and 12TB (non-SMR) drives for our ever expanding preloaded data files. Based on your comment we will stay away from SMR for now. It definitely seem to be a work in progress...

Any other comments about the progress of development of SMR support would still be appreciated.
 
dkline201 said:
Based on your comment we will stay away from SMR for now. It definitely seem to be a work in progress...
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No, don't do that! Just because I haven't heard about the state of the art, it doesn't imply that the art is not very progressed. It is possible that there are file systems available that are SMR-aware enough to have good performance. You'll have to do your own research though. It is very clear from discussions in academia and industry that software support for SMR is currently a work in progress. But that doesn't necessarily imply that the work isn't usable yet.

(Funny anecdote: I'm sitting right now in the auditorium of the FAST 2018 conference in Oakland, California, where the community of File system and Storage Technologies is assembled. There is certainly someone in the room who could answer your question specific to the FreeBSD file systems, but I'm too busy to find them, and there are lots of people here.)
 
Heard yesterday: For Linux, there is a modification of the ext4 file system that is SMR-aware. That work was done by a CMU graduate student under the guidance of Garth Gibson (who is now in Toronto at the machine learning institute) and Ted Ts'o (who is now at Google), and a description of that work was published in the Usenix login magazine and presented at the FAST conference a year ago. But what I couldn't find out quickly is whether the changes for SMR were ever put into a mainstream ext4 release, or whether they

For FreeBSD, Adrian Palmer of Seagate has worked on making ZFS and UFS (or FFS) SMR-aware, but I don't know how far that work progressed.

Warning: I didn't actually talk to any of these people themselves, this is all second-hand; you'll have to find the details yourself.
 
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