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Hi Coly and all,
I found there is an error message in our testing:
Sep 27 17:43:00 node-1 kernel: bcache: error on
c2914b7e-d665-4ec1-80e1-272755de19ef: unsupported bset version at bucket
58290, block 0, 40818810 keys, disabling caching
I checked the code in bch_btree_node_read_done() around this message:
214 for (;
215 b->written < btree_blocks(b) && i->seq == b->keys.set[0].data->seq;
216 i = write_block(b)) {
217 err = "unsupported bset version";
218 if (i->version > BCACHE_BSET_VERSION)
219 goto err;
220
The problem is we found the i->seq is what we expected for this btree_node, but the version is not BCACHE_BSET_VERSION (1)
I think there would be two reasons to cause this messages:
(1) cache discard is not enabled.
When we allocate a bucket, if we dont enable discard, there could be some outdated data in this bucket,
and there is possibility that the location of i->seq is equal to what we expected,
but that's really not an bset at all, so we will found version, magic and bset_csum are all unexpected,
currently we will goto err and stop cache_set.
(2) power-cut.
When we are doing btree_node_write, if there is a power-cut happen, we could write a partial btree.
But when we meet this kind of problems, we cant use this cache device. There is no tool to recovery from this kind of problem.
I think I can cook a bcache-check in bcache-tools, something like fsck. to check this kind of problem
and allow user to repair it, warning on user force-repaire is risky.
Please help to point out if there is something I am missing.
Thanx
Dongsheng
