On 02/07/2014 02:00 PM, Carlos Maiolino wrote: > Hi, > > On Sat, Feb 01, 2014 at 02:24:33AM +0000, Albert Chen wrote: >> [LSF/MM TOPIC] SMR: Disrupting recording technology meriting >> a new class of storage device >> >> Shingle Magnetic Recording is a disruptive technology that >> delivers the next areal density gain for the HDD industry by >> partially overlapping tracks. Shingling requires physical >> writes to be sequential, and opens the question of how to >> address this behavior at a system level. Two general approaches >> contemplated are to either to do the block management in >> the device or in the host storage stack/file system through >> Zone Block Commands (ZBC). >> >> The use of ZBC to handle SMR block management yields several >> benefits such as: >> - Predictable performance and latency >> - Faster development time >> - Access to application and system level semantic information >> - Scalability / Fewer Drive Resources >> - Higher reliability >> >> Essential to a host managed approach (ZBC) is the openness of >> Linux and its community is a good place for WD to validate and >> seek feedback for our thinking - where in the Linux system stack >> is the best place to add ZBC handling? at the Device Mapper layer? >> or somewhere else in the storage stack? New ideas and comments >> are appreciated. > > If you add ZBC handling into the device-mapper layer, aren't you supposing that > all SMR devices will be managed by device-mapper? This doesn't look right IMHO. > These devices should be able to be managed via DM or either directly via de > storage layer. And any other layers making use of these devices (like DM for > example) should be able to communicate with them and send ZBC commands as > needed. > Precisely. Adding a new device type (and a new ULD to the SCSI midlayer) seems to be the right idea here. Then we could think of how to integrate this into the block layer; eg we could identify the zones with partitions, or mirror the zones via block_limits. There is actually a good chance that we can tweak btrfs to run unmodified on such a disk; after all, sequential writes are not a big deal for btrfs. The only issue we might have is that we might need to re-allocate blocks to free up zones. But some btrfs developers have assured me this shouldn't be too hard. Personally I don't like the idea of _having_ to use a device-mapper module for these things. What I would like is giving the user a choice; if there are specialized fs around which can deal with such a disk (hello, ltfs :-) then fine. If not of course we should be having a device-mapper module to hide the grubby details for unsuspecting filesystems. Cheers, Hannes -- Dr. Hannes Reinecke zSeries & Storage hare@xxxxxxx +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg) -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
