Unable to mount hammer file system Undo failed

[Wojciech Puchar]

>> not great.
>
> This is not a hammer problem but a problem with the underlying disk. It
> couldn't read from the disk - that is pretty much a file-system
> independent problem; UFS would fail equally miserably.
not true.
it is very unlinkey case you will not be able to mount. you will not be 
able to read everything.

copying to new disks with skipping errors (dd conv=sync,noerror) and doing 
fsck_ffs basically would recover everything that can be recovered.

UFS use flat on disk structure. inodes are at known places.

I don't know how HAMMER data is placed, but seems everything is dynamic.

any link to description of HAMMER on disk layout?