Jari Ruusu wrote: > Both device sizes are integer multiples of 4096 bytes. When you shrink the > the device size by non-4096 byte amount, that is no longer true. 976773160 > and 976773168 sector size devices can be fully accessed using 4096 soft > block size. It is the default smaller soft block size that causes the > slowdown. Just to clarify this: Default soft block size is set to such value that full device can be accessed using X amount of such soft block size chunks. File system mount knows that it won't access any less-than-block-size leftovers at the end of the device, so it can set to more sane value. In following examples, /dev/hdd2, /dev/loop3 and /dev/loop6 sizes are interger multiple of 4096 bytes, and as such, can be fully accessed using 4096 byte soft block size. /dev/hdd9, /dev/loop4 and /dev/loop5 are not, and are accessed using 512 byte soft block size. Prior to mount, that is. Meaning that any mkfs, fsck, and other direct access will not perform as fast and efficiently as for /dev/hdd2, /dev/loop3 and /dev/loop6. After mount, /dev/hdd2 and /dev/hdd9 should perform identically, as should /dev/loop3, /dev/loop4, /dev/loop5 and /dev/loop6. # blockdev --getsize /dev/hdd2 102816 (device size is integer multiple of 4096 bytes) # losetup -e AES128 -K loop-AES/gpgkey3.asc /dev/loop3 /dev/hdd2 Password: # blockdev --getbsz /dev/loop3 4096 (default soft block size is 4096 bytes) # losetup -e AES128 -K loop-AES/gpgkey3.asc -o 512 /dev/loop5 /dev/hdd2 Password: # blockdev --getbsz /dev/loop5 512 (default soft block size is *LESS THAN* 4096 bytes) # blockdev --getsize /dev/hdd9 102753 (device size is *NOT* integer multiple of 4096 bytes) # losetup -e AES128 -K loop-AES/gpgkey3.asc /dev/loop4 /dev/hdd9 Password: # blockdev --getbsz /dev/loop4 512 (default soft block size is *LESS THAN* 4096 bytes) # losetup -e AES128 -K loop-AES/gpgkey3.asc -o 512 /dev/loop6 /dev/hdd9 Password: # blockdev --getbsz /dev/loop6 4096 (default soft block size is 4096 bytes) -- Jari Ruusu 1024R/3A220F51 5B 4B F9 BB D3 3F 52 E9 DB 1D EB E3 24 0E A9 DD - Linux-crypto: cryptography in and on the Linux system Archive: http://mail.nl.linux.org/linux-crypto/
