HAMMER filesystem check / CRC verification

Tomohiro Kusumi kusumi.tomohiro at gmail.com
Fri Jan 22 07:57:18 PST 2016

If you are to redirect the hammer show output to a file, it's better to
write to a file on different filesystem (e.g. ufs or another hammer).

It's possible that hammer show never ends because what hammer show does is
run through all ondisk btree nodes. Writing a file is adding nodes into the
btree of that filesystem.

2016-01-23 0:44 GMT+09:00 Tomohiro Kusumi <kusumi.tomohiro at gmail.com>:

> (resending as i forgot to send to users at ...)
> # hammer -v -f ${DEV} blockmap
> # hammer -v -f ${DEV} checkmap
> # hammer -v -f ${DEV} show
> These three do some validation from different point of view.
> If the last two lines of each output says 0 error, then no error was found
> at least by what these 3 commands test for.
> Note that there seems to be a bug in hammer where a valid filesystem would
> still show ^B in hammer show output. I usually run some test scripts (that
> contain there 3 commands) before I commit something, but I see ^B in hammer
> show every once in a while. It could be that the way hammer show tests the
> filesystem is missing something and results in showing errors that aren't
> really errors. This occurred at least back in DragonFly 4.0 era in 2014,
> and it still does on 4.4. It has been on my todo list for a long time.
> 2016-01-22 23:59 GMT+09:00 PeerCorps Trust Fund <ipc at peercorpstrust.org>:
>> Hi All,
>> In ZFS, the command "zpool status" gives a succinct overview of the
>> status of mounted file systems. In particular, whether there might be
>> checksum errors on files or other data structures.
>>         NAME        STATE     READ WRITE CKSUM
>>         tank        ONLINE       0     0     0
>>           ada0p2    ONLINE       0     0     0
>> In HAMMER the "show" command provides an extremely detailed output of all
>> data structures and CRC verifications.
>> I've used the command:
>> hammer -f /dev/serno/disk-serial-number show |grep B------
>> On a mounted disk and the output was clean (nothing) after running for
>> some time with noted disk activity. Does this mean that all CRCs are valid?
>> Are there other commands in addition to "show" that allow for validation
>> and examination of data structures on HAMMER volumes?
>> --
>> Mike
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