[dm-crypt] status of dm-crypt (alignment issues) on a SSD

Milan Broz mbroz at redhat.com
Thu Dec 2 12:44:13 CET 2010

On 12/02/2010 08:54 AM, Luca Berra wrote:

> what you need on kernel side is having in sysfs
> under /sys/block/<device>
> queue/minimum_io_size
> queue/optimal_io_size
> queue/physical_block_size

Just not all SSD presents proper values here.

My advice is align to 1MiB in such case and it will work:-)
(this is default in recent versions - not all yet in Debian)

You can always do it manually, use fdisk -u (to work in sector mode,
note sector is 512B. Switch off DOS mode if it is enabled - there
should be warning)

For lvm, use pvcreate --dataalignment, then check with pvs -o +pe_start.
(You can use --units S to work in sectors mode like in fdisk.
2048 sectors == 1MiB, any multiple of it is ok)

(See man page and check archive, I think it was described here
several times.)


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