Unable to mount hammer file system Undo failed

[Wojciech Puchar]

> HAMMER(ROOT) recovery check seqno=8ca97e62
> HAMMER(ROOT) recovery range 3000000006877528-3000000006892fa0
> HAMMER(ROOT) recovery nexto 3000000006892fa0 endseqno=8ca98015
> HAMMER(ROOT) recovery undo  3000000006877528-3000000006892fa0 (113272 bytes)(RW)
> ad4: FAILURE - READ_DMA48 status=51<READY,DSC,ERROR>
> error=40<UNCORRECTABLE> LBA=483752928
> HAMMER: UNDO record, cannot access buffer 2000003436e35ca8
> HAMMER(ROOT) UNDO record at 3000000006891a30 failed
> HAMMER(ROOT) recovery complete
> Failed to recover HAMMER filesystem on mount
>
this is example of what i fear about hammer. One error results in 
unability to mount.

If it is just software error in hammer that's great. If it is design... 
not great.