Hi Jim, On Fri, Feb 07, 2014 at 05:32:44PM +0000, Jim Malina wrote: > > > > -----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. >
Thanks for clarification, and, this just enforce my concept that ZBC protocol should be integrated in the generic block layer not make it device-mapper dependent. So, make this available to any device that supports it with or without the help of DM. > > 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-fsdevel" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Carlos -- 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
