Hi Roscoe,
let me quote from the man page (which of course could be wrong):
--align-payload=value
Align payload at a boundary of value 512-byte sectors.
This
option is relevant for luksFormat. If your block device
lives
on a RAID, it is useful to align the filesystem at full
stripe
boundaries so it can take advantage of the RAID's geometry.
See
for instance the sunit and swidth options in the mkfs.xfs
manual
page. By default, the payload is aligned at an 8 sector
(4096
byte) boundary.
----
If it is meant to align payload for raid devices it would be really fatal
if it modifies the value and thus data is not aligned. As far as I
understand it, luks will need at least 8 sectors (4KB) for the header
data. Sine I specificly demanded 2048 sectors (1MB) the value for the
offet should be no problem at all. Further investigation showed, that (my
impression) cryptsetup uses the underlying blockdevice's readahead, which
is certainly the wrong way to determine the payload offset value.
Regards
-Sven
On Sat, July 18, 2009 03:12, Roscoe wrote:
> On 7/18/09, Sven Eschenberg <sven@xxxxxxxxxxxxxxxxxxxxx> wrote:
>> Hi list,
>>
>> when trying to luksFormat a device with: --align-payload=2048 and thus
>> moving the payload to 1MB from the beginning of the underlying device,
>> luksDump outputs the following:
>> Payload offset: 4096 (?)
>>
>> This does not seem to make any sense.
>
> Perhaps the option means align at a 2048 boundary, thus 2048, or 4096,
> or 6144, etc...
> It I imagine picked the first boundary that wouldn't result in
> overwriting of the keyslots.
>
> -- Roscoe
>
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