On Friday 12 March 2010 10:15:28 Stephan von Krawczynski wrote: > On Fri, 12 Mar 2010 02:07:40 +0100 > > Hubert Kario <h...@qbs.com.pl> wrote: > > > [...] > > > If the FS were to be smart and know about the 256kb requirement, it > > > would do a read/modify/write cycle somewhere and then write the 4KB. > > > > If all the free blocks have been TRIMmed, FS should pick a completely > > free erasure size block and write those 4KiB of data. > > > > Correct implementation of wear leveling in the drive should notice that > > the write is entirely inside a free block and make just a write cycle > > adding zeros to the end of supplied data. > > Your assumption here is that your _addressed_ block layout is completely > identical to the SSDs "disk" layout. > Else you cannot know where a "free > erasure block" is located and how to address it from FS. > I really wonder what this assumption is based on. You still think a SSD is > a true disk with linear addressing. I doubt that very much.
I made no such assumptions. Im sure that the linearity on the ATA LBA level isn't so linear on the device level, especially after wear-leveling takes its toll, but I assume that the smallest block of data that the translation layer can address is erase-block sized and that all the erase-block are equal in size. Otherwise the algorithm would be needlessly complicated which would make it both slower and more error prone. > Even on true > spinning disks your assumption is wrong for relocated sectors. Which we don't have to worry about because if the drive has less than 5 of 'em, the impact of hitting them is marginal and if there are more, the user has much more pressing problem than the performance of the drive or FS. > Which > basically means that every disk controller firmware fiddles around with > the physical layout since decades. Please accept that you cannot do a > disks' job in FS. The more advanced technology gets the more disks become > black boxes with a defined software interface. Use this interface and drop > the idea of having inside knowledge of such a device. That's other > peoples' work. If you want to design smart SSD controllers hire at a > company that builds those. And I don't think that doing disks' job in the FS is good idea, but I think that we should be able to minimise the impact of the translation layer. The way to do this, is to threat the device as a block device with sectors the size of erase-blocks. That's nothing too fancy, don't you think? -- Hubert Kario QBS - Quality Business Software ul. Ksawerów 30/85 02-656 Warszawa POLAND tel. +48 (22) 646-61-51, 646-74-24 fax +48 (22) 646-61-50 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
