Roscoe wrote: > On Sat, Jul 18, 2009 at 7:04 PM, Sven > Eschenberg<sven@xxxxxxxxxxxxxxxxxxxxx> wrote: >> Sorry for answering my own mail, >> >> I had a misconception there. I fired various values for dataalignment at >> cryptsetup and it always chose a value of n*DA >= 4096 sectors. So >> obviously 4096 sectors seems to be a lower bound I was not aware of. >> > You may be underestimating the space LUKS takes up. The PHDR is 592 > bytes, but the keyslot sizes depend on the number of AFstrips and the > keysize. If one us using AES-256 with XTS and 4000 strips, then the > space LUKS takes up will be around 2 megabytes. Exactly, moreover keyslots are aligned to 4k blocks too. You can check the real data offset in luksDump (Payload offset). The --align-payload takes argument in sectors (512 bytes) and the real data alignment is rounded up to multiply of that. For example, default alignement is 4k with 128bit key you get: data offset 1032 sectors With --align-payload=512 you get data offset 1536 (3 * 512). Milan p.s. BTW For LVM over LUKS I mostly use 4MB (Which always aligns to my underlying SSD drive, the same applies to underlying RAID and chunk/stripe size) - properly align partition (use sectors, not default: fdisk -u, or use parted) - align data on LUKS drive (e.g. cryptsetup luksFormat ... --align-payload=8192 to align to 4MB) - pvcreate --dataalignment 4M to align PV to 4M offset, all LVs will be aligned automagically when created (option available in recent lvm2) --------------------------------------------------------------------- dm-crypt mailing list - http://www.saout.de/misc/dm-crypt/ To unsubscribe, e-mail: dm-crypt-unsubscribe@xxxxxxxx For additional commands, e-mail: dm-crypt-help@xxxxxxxx
