> On May 24, 2017, at 6:39 PM, Andrew Gabriel <[email protected]> > wrote: > > On 24/05/2017 22:10, Ken Merry wrote: >> Is anyone working on SMR support for ZFS? >> >> I put support into FreeBSD for SMR drives from the block layer (GEOM) >> through the SCSI layer (CAM): >> >> https://svnweb.freebsd.org/base?view=revision&revision=300207 >> >> So far, no filesystems in the FreeBSD tree are using the SMR support. >> >> It looks like there are Linux folks working on SMR support: >> >> http://events.linuxfoundation.org/sites/events/files/slides/lemoal-Linux-SMR-vault-2017.pdf >> >> We (Spectra Logic) are considering starting work on supporting Host Aware >> and Host Managed SMR drives in ZFS, and we’d rather collaborate with other >> folks who are interested instead of duplicating the effort. > > There was a discussion about it at the European OpenZFS conference in Paris a > couple of years ago. One of the drive vendors came along and gave a technical > presentation on SMR, with a view to persuading ZFS developers to modify ZFS > to make good use of SMR drives. > > The presentation was very good, but the general feedback at the time was that > no one believed SMR would be around for very long, probably not long enough > to get any support in ZFS stable, before hard drives had completely given way > to SSDs. > > Things may have changed since then, although I hear less about SMR drives now > than I did back then. How long do you think SMR will be around? What is your > use case for the drives?
Spectra’s take on it is that Seagate and HGST / WD will likely keep producing high capacity SMR drives for a while. >From a logical standpoint, SMR allows them to increase the drive capacity by >20% or so (the numbers are fuzzy, that isn’t a precise amount), and they’ve >been selling SMR drives for a lower cost per GB than traditional fully random >access drives. SSD prices are coming down, and capacity is going up, but it still can’t match hard drives in terms of price for the capacity. On the other end of the spectrum, tape capacity and throughput is increasing pretty rapidly. (LTO-8 is coming soon.) In between those is spinning disk. SMR disks have lower random write performance, but also lower price, and are more competitive with tape. With tape capacity increasing, the disk vendors will want to stay somewhat competitive. SMR is a tool that they can use to compete on the lower price, higher capacity end of the spectrum. Spectra’s focus is generally on archive and backup storage. That means high capacity disk and tape libraries. Spectra generally only uses SSDs for things like caching, databases, etc. They’re too expensive for archive storage. As for Spectra’s use case for the drives: https://www.spectralogic.com/products/arcticblue/ <https://www.spectralogic.com/products/arcticblue/> That’s a 96-drive, 4U JBOD enclosure. We can put up to 8 Arctic Blue enclosures behind a Black Pearl (S3) box. Right now we’re using Drive Managed SMR drives with ZFS. We only had to do some minor modifications to ZFS to get reasonable performance with Drive Managed SMR drives. The cost (as low as $.10/GB for the whole system) is very good. While one vendor has Drive Managed and Host Aware drives, the other one, as far as I know, only has Host Managed drives. Host Managed is much harder to deal with from a software standpoint, since it can’t handle any out of order access within the bands. In order to have higher performance with Host Aware drives, and be able to choose between vendors, we’ll have to implement Host Managed support in ZFS, or write a layer below ZFS that will do read/modify/write to eliminate any non-sequential writes to Host Managed disks. Ken — Ken Merry [email protected] ------------------------------------------ openzfs-developer Archives: https://openzfs.topicbox.com/groups/developer/discussions/T1fec2160a70daccc-M63c1e798a0c2c95b02d82ed9 Powered by Topicbox: https://topicbox.com
