Den ons 6 maj 2020 kl 00:58 skrev Oliver Freyermuth < freyermuth@physik.uni-bonn.de>:
Dear Cephalopodians, seeing the recent moves of major HDD vendors to sell SMR disks targeted for use in consumer NAS devices (including RAID systems), I got curious and wonder what the current status of SMR support in Bluestore is. Of course, I'd expect disk vendors to give us host-managed SMR disks for data center use cases (and to tell us when actually they do so...), but in that case, Bluestore surely needs some new intelligence for best performance in the shingled ages.
I've only done filestore on SMRs, and it did work for a while, in normal cases for us, but it broke down horribly as soon as recovery needed to be done. I have no idea if filestore was doing the worst ever for SMRs, or if bluestore will do better or if patches are going to help bluestore become useful, but all in all, I can't say anything else to people wanting to experiment with SMRs than "if you must use SMRs, make sure you test the most evil of corner cases". As you noted, one can easily get into <1M/s with SMRs by doing something else than long linear writes, and you don't want to be in a place where several hundred TBs of data is doing recovery at that speed. To me, SMR is a con, its a trick to sell cheap crap to people who can't or won't test properly. Doesn't matter if its ceph recovery/backfill, btrfs deletes or someones NAS raid sync job that places the final straw on the camels back and breaks it, it's the fact that filesystems do lots more than just easy nice long linear writes. No matter if it is fsck, defrags or ceph PG splits/reshardings, there will be disk meta-operations that needs to be done which includes tons of random small writes, and SMR drives will punish you for them when you need the drive up the most. 8-( If I had some very special system which used cheap disks to pretend to be a tape device and only did 10G sized reads/writes like a tape would do, then I could see a use case for SMR. -- May the most significant bit of your life be positive.