Stefan Monnier put forth on 1/11/2011 10:28 PM: > Isn't it rather than the kernel chooses to only use the logical > sector size? Where/when does the drive report 512B physical > sector sizes?
Read the ATA and SCSI specifications. Or ask on either mailing list. In short, the drive presents its LBA addressing based on 512B sectors. The kernel can't choose to ignore that--it's stuck with it. Since the drive is presenting LBA based on 512B sectors, there is no way the kernel can address LBA based on 4K sectors. > In any case, the issue is probably not really in the kernel but in the > filesystems and partitioning tools: all that's really needed to use the The problem is none of those things. The problem is hybrid drives. IIRC, the kernel, libata, libscsi, etc, are all ready for _native_ 4K sector drives. The current "problem" with the hybrid drives is that the partitioning utilities don't automatically align partitions on the underlying 4k sector boundaries. So, what happens is, in essence, when a filesystem is laid down that uses 4K blocks, it will lay across 4 _translated_ 512B sectors. Thus, you end up with a 4K filesystem block that lays across two physical 4K disk sectors. Thus, each time that FS block is written, 8*512B sectors must be read and re-written. Thus, _TWO_ physical 4K disk sectors must be read and re-written instead of just one on an aligned partition, akin to the the RAID5/6 read/modify/write penalty. This misalignment cuts performance by half or more because every FS block write requires to reads and two writes instead of just one. > drive efficiently is for fdisk/parted and for mkfs to be told (and make > use of) the physical block size. Of course, maybe a good way to provide > this info is to teach the kernel about it so those tools don't need to > use side-band info via hdparm. Maybe you should hit the LKML, GNU fdisk, and GNU parted list archives before continuing this thread. > Indeed, and for that reason 4KB physical blocks wouldn't cause > additional disk space usage. The space savings with 4KB sectors has nothing to do with file systems or user data. It has to do with the per sector ECC information that all drives calculate and store in between sectors to safeguard the data in the sector. The number of bits of ECC required per 4KB sector is significantly less than that occupied by the 4 ECC segments of four 512 byte sectors. This is the ONLY reason these 4KB sector drives were developed: more actual end user space on the drive. -- Stan -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/4d2def0f.1080...@hardwarefreak.com
