The original post asks how to do if the superblock was broken (his superblock
was accidentally wiped). Since that I don't have time to update the program
at this moment, here's my workaround:
1. Partially rebuild the superblock
(1) Obtain pool parameter from LVM
./sbin/lvm lvs vg1/tp1 -o transaction_id,chunksize,lv_size --units s
sample output:
Tran Chunk LSize
3545 128S 7999381504S
The number of data blocks is $((7999381504/128)) = 62495168
(2) Create input.xml with pool parameters obtained from LVM:
<superblock uuid="" time="0" transaction="3545"
data_block_size="128" nr_data_blocks="62495168">
</superblock>
(3) Run thin_restore to generate a temporary metadata with correct superblock
dd if=/dev/zero of=/tmp/test.bin bs=1M count=16
thin_restore -i input.xml -o /tmp/test.bin
The size of /tmp/test.bin depends on your pool size.
(4) Copy the partially-rebuilt superblock (4KB) to your broken metadata.
(<src_metadata>).
dd if=/tmp/test.bin of=<src_metadata> bs=4k count=1 conv=notrunc
2. Run thin_ll_dump and thin_ll_restore
https://www.redhat.com/archives/linux-lvm/2016-February/msg00038.html
Example: assume that we found data-mapping-root=2303
and device-details-root=277313
./pdata_tools thin_ll_dump <src_metadata> --data-mapping-root=2303 \
--device-details-root 277313 -o thin_ll_dump.txt
./pdata_tools thin_ll_restore -E <src_metadata> -i thin_ll_dump.txt \
-o <dst_metadata>
Note that <dst_metadata> should be sufficient large especially when you
have snapshots, since that the mapping trees reconstructed by thintools
do not share blocks.
3. Fix superblock's time field
(1) Run thin_dump on the repaired metadata
thin_dump <dst_metadata> -o thin_dump.txt
(2) Find the maximum time value in data mapping trees
(the device with maximum snap_time might be remove, so find the
maximum time in data mapping trees, not the device detail tree)
grep "time=\"[0-9]*\"" thin_dump.txt -o | uniq | sort | uniq | tail
(I run uniq twice to avoid sorting too much data)
sample output:
...
time="1785"
time="1786"
time="1787"
so the maximum time is 1787.
(3) Edit the "time" value of the <superblock> tag in thin_dump's output
<superblock uuid="" time="1787" ... >
...
(4) Run thin_restore to get the final metadata
thin_restore -i thin_dump.txt -o <dst_metadata>
Ming-Hung Tsai
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