Mounting a filesystem on a HAST provider without HAST (was: Re: HAST, zvols, istgt and carp working...)
to.my.trociny at gmail.com
Sat Nov 29 12:31:35 UTC 2014
On Fri, Nov 28, 2014 at 12:21:05PM +0100, Lorenzo Perone wrote:
> The UFS filesystem on the zvol provider begins after 135168 bytes
> (132KB) of hast-header.
> So I tried to create a transparent provider with gnop:
> gnop create -o 135168 /dev/zvol/rtank/vols/jail1 at hellotest
> and the mount
> mount -t ufs -o ro /dev/zvol/rtank/vols/jail1 at hellotest.nop /mnt
> Now my new question is: Can I "safely" assume that this header is always
> 132K (I assume not - it probably contains the bitmap...)? In this case,
> which formula should be applied to calculate the offset?
The header contains 4096 bytes of HAST metadata (METADATA_SIZE) + map,
which size depends on media size and extent size.
You can obtain the offset by running `hastctl dump' command (localcnt
If you still want to calulate it yourself, see how hastctl calculates
hr_localoff in sbin/hastctl/hastctl.c:create_one() with the help of
sbin/hastd/metadata.c:activemap_calc_ondisk_size(). In short, you need
to calculate number of extents (mediasize / extentsize) and reserve a
bit for every extent in the map, rounding up to the sector size.
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