[dm-crypt] Does luksFormat write the full size of the device?

Milan Broz gmazyland at gmail.com
Sun Jun 26 12:46:43 CEST 2016

On 06/26/2016 05:39 AM, Charles Cazabon wrote:
> Hi,
> I'm currently initializing a fairly large LUKS crypt device, about 33TiB.
> I've done this before, but not for quite a while, so I can't remember how long
> it normally takes.  My current cryptsetup invocation has been running for
> about 24 hours, taking 100% of one CPU core for that entire time.  If there's
> I/O happening, iostat isn't showing it.
> If `cryptsetup luksFormat` has to write the entire contents of the underlying
> block device, then this length of time is reasonable - but I don't recall if
> it has to do that.

No, format doesn't write the whole device.

Can you please post output of running commant with added --debug switch?
(Just up to point it starts to eat CPU cycles.)

(I think it loops in PBKDF2 benchmark, I have seen some unexpected breakage
here with recent kernel, but without debug log it is just guess.)

> Is this long runtime normal for initialization of a device of this size?

No. If the default iteration time (1 or 2 seconds) is not changes, format should
be done in max 4-5 seconds.


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