> -----Original Message----- > From: Hannes Reinecke [mailto:h...@suse.de] > Sent: Friday, February 07, 2014 5:46 AM > To: Carlos Maiolino; Albert Chen > Cc: lsf...@lists.linux-foundation.org; James Borden; Jim Malina; Curtis > Stevens; linux-...@vger.kernel.org; linux-fsde...@vger.kernel.org; linux- > s...@vger.kernel.org > Subject: Re: [LSF/MM TOPIC] SMR: Disrupting recording technology meriting > a new class of storage device > > 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. > >
Clarification: ZBC is an interface protocol. A new device and command set. SMR is a recording technology. You may have ZBC without SMR or SMR without ZBC. For examples. SSD may benefit from ZBC protocol to improve performance and reduce wear. SMR may be 100% device managed and not provide information required of a ZBC device, like write pointers or zone boundaries. > 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 > h...@suse.de +49 911 74053 688 > SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg > GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg) jim -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
