On Fri, Oct 26, 2012 at 8:54 PM, Vladislav Bolkhovitin <v...@vlnb.net> wrote:
> > Theodore Ts'o, on 10/25/2012 01:14 AM wrote: > >> On Tue, Oct 23, 2012 at 03:53:11PM -0400, Vladislav Bolkhovitin wrote: >> >>> Yes, SCSI has full support for ordered/simple commands designed >>> exactly for that task: to have steady flow of commands even in case >>> when some of them are ordered..... >>> >> >> SCSI does, yes --- *if* the device actually implements Tagged Command >> Queuing (TCQ). Not all devices do. >> >> More importantly, SATA drives do *not* have this capability, and when >> you compare the price of SATA drives to uber-expensive "enterprise >> drives", it's not surprising that most people don't actually use >> SCSI/SAS drives that have implemented TCQ. >> > > What different in our positions is that you are considering storage as > something you can connect to your desktop, while in my view storage is > something, which stores data and serves them the best possible way with the > best performance. > > Hence, for you the least common denominator of all storage features is the > most important, while for me to get the best of what possible from storage > is the most important. > > In my view storage should offload from the host system as much as > possible: data movements, ordered operations requirements, atomic > operations, deduplication, snapshots, reliability measures (eg RAIDs), load > balancing, etc. > > It's the same as with 2D/3D video acceleration hardware. If you want the > best performance from your system, you should offload from it as much as > possible. In case of video - to the video hardware, in case of storage - to > the storage. The same as with video, for storage better offload - better > performance. On hundreds of thousands IOPS it's clearly visible. > > Price doesn't matter here, because it's completely different topic. > > > SATA's Native Command >> Queuing (NCQ) is not equivalent; this allows the drive to reorder >> requests (in particular read requests) so they can be serviced more >> efficiently, but it does *not* allow the OS to specify a partial, >> relative ordering of requests. >> > > And so? If SATA can't do it, does it mean that nobody else can't do it > too? I know a plenty of non-SATA devices, which can do the ordering > requirements you need. > I would be very much interested in what kind of device support this kind of "topological order", and in what settings they are typically used. Does modern flash/SSD (esp. which are used on smartphones) support this? If you could point me to some information about this, that would be very much appreciated. Thanks a lot! Suli > > Vlad > > -- > 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<http://vger.kernel.org/majordomo-info.html> > _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
