Re: [BackupPC-users] Verify full integrity of pool and backups

Hi,

another update from my side, for all who might be interested / future 
generations ;-)

I set $Conf{PoolNightlyDigestCheckPercent} = 100
and ran BackupPC_refCountUpdate -m .

I get 104 ERRORs with md5sum d41d8cd98f00b204e9800998ecf8427e (= empty 
file) instead of the expected digest.  All of these files have 0 length, 
see https://paste.ubuntu.com/p/RRBSsXvMWV/

My observations until now:

A. The timestamp of these files falls into 1 of 3 dates, see 
https://paste.ubuntu.com/p/FcY3gb5q8V/ (sorted via xargs ls -altr)
If I disregard the 2 files from 2017, these files first started to 
appear when I upgraded rsync-bpc from 3.0.9.14 to 3.0.9.15
(I usually initate a test backup right after an upgrade to validate 
everything is functioning correctly)

> /var/log/dpkg.log: 2020-08-12 22:46:22 upgrade rsync-bpc:amd64 3.0.9.14 
> 3.0.9.15


B. I verified that there are no other pool files with the same digest 
(so no digest* / digest + extension).


C. At least some of these pool files are related to attrib files, i.e.
> BackupPC_attribPrint 
> aaa.aaa.aaa/8238/f%2fdata%2fmail%2f/fspool/attrib_f1811600a7b6f6e3f2fcafea644e005b
> BackupPC_attribPrint: cannot read attrib file 
> mail.bhatia.eu/8238/f%2fdata%2fmail%2f/fspool/attrib_f1811600a7b6f6e3f2fcafea644e005b 
> (f1811600a7b6f6e3f2fcafea644e005b)


D. Looking at the source of rsync-bpc, I find: 
https://github.com/backuppc/rsync-bpc/blob/3.0.9/backuppc/bpc_poolWrite.c#L348 
and 
https://github.com/backuppc/rsync-bpc/commit/3eb30d1b4fe844d0a1409f8a090c518e4d713f40#diff-11e5a98fabcaf3b4938189c693342209 
.  Could this play a role here?


(I have to admit that I am not (yet?) able to wrap my head around the 
pooling, so please excuse any error in my assuptions.)

-->
1. To me, this reads in a way that backuppc might (have?) decide(d) to 
zero out a file / create an empty pool file?

2. Would it make sense to handle this specific case (empty pool file) in 
BackupPC_refCountUpdate when checking the pool, i.e. at 
https://github.com/backuppc/backuppc/blob/master/bin/BackupPC_refCountUpdate#L821


Any further help to debug this problem would be appreciated!
Raoul
PS. Cross-posting to backuppc-devel mailing list, just in case.

On 2020-08-27 21:58, Raoul Bhatia wrote:
> Hi Craig, Guillermo, all.
> 
> A quick update from my side
> 
> I have a (complete?) list of (potentially) broken files as reported by
> BTRFS read errors.
> 
> I then validated the md5sum from the (c)pool with a one-liner:
>> for i in $(grep /cpool/ ~/broken_files.txt); do 
>> M=$(/usr/share/backuppc/bin/BackupPC_zcat $i | md5sum | cut -d ' ' -f 
>> 1); echo -n "$M: "; echo $i | grep --color $M || echo "$f ERR"; done
> --> No error, perhaps I am lucky? :-)
> 
> 
> This leaves only one file that might be damaged:
> backuppc/pc/abc.def.ghi/1989/refCnt/poolCnt.1.16 ?
> 
> I am now experimenting with running
> /usr/share/backuppc/bin/BackupPC_refCountUpdate -m
> (Until now: No error; exit code 0)
> 
> 
> 
> Reading the source I have the following questions:
> 
> 1.
> https://github.com/backuppc/backuppc/blob/master/bin/BackupPC_refCountUpdate#L819
> does "rand(100) < $Conf{PoolNightlyDigestCheckPercent}"
> 
> My understanding would be that I won't get a predictable 1% check on
> *each* run.  Perhaps on average, with a sufficiently large pool, over
> a longer period of time, this might work out, but for a few runs of
> BackupPC_refCountUpdate not.
> 
> --> Perhaps there would be another implementation that gets a more
> predictable result?
> (i.e. create an array of all the files to check, sort them, and then
> take the first $Conf{PoolNightlyDigestCheckPercent} of entries, but at
> least 1?)
> 
> 
> 
> 2. I also seem to have accumulated checksum errors over the past years.
> 
> --> How do I proceed with these files?  If they still exist on the
> source, I'd like to re-sync them to the backup.
> 
> 
> 3. For backuppc/pc/abc.def.ghi/1989/refCnt/poolCnt.1.16 , I do not
> find a way to re-check only this one, old backup.
> 
> --> Would it be a good idea to add an option to add a "-n num" flag to
> BackupPC_refCountUpdate to be able to operate on a particular backup?
> 
> 
> 
> Thanks for your guidance,
> Raoul
> 
> On 2020-08-24 20:39, Raoul Bhatia wrote:
>> Hi Craig and Guillermo,
>> 
>> On 2020-08-23 19:35, Craig Barratt via BackupPC-users wrote:
>> 
>>> $Conf{PoolNightlyDigestCheckPercent} is in percent, so you should set 
>>> it to 100 to check all the pool file's MD5 digest against their file 
>>> names.
>>> 
>>> As Guillermo mentions, to check the pool MD5 digests, you can set 
>>> temporarily set $Conf{PoolNightlyDigestCheckPercent} to 100 and 
>>> $Conf{PoolSizeNightlyUpdatePeriod} to 1.
>> 
>> When reading the documentation, I also came across these options.
>> However, I didn't dare to run backuppc / BackupPC_nightly, because
>> from the documentation:
>> 
>>    Overnight, when BackupPC_nightly next runs,
>>    all the unused pool files will be deleted and
>>    this will recover the disk space used by the client's backups.
>> 
>> I didn't want to end up with an empty pool...
>> 
>>> If you stop BackupPC, to check all the pool digests, run:
>>> 
>>>> BackupPC_refCountUpdate -m
>>> If you want to also regenerate all the host reference counts (which 
>>> will take a long time), you could run:
>>> 
>>>> BackupPC_refCountUpdate -m -F
>> 
>> Meanwhile, with the kind help of the btrfs community, I figured out a
>> way to get the damaged files.  This process is not finished, yet,
>> however, I have a first list:
>> 
>> /mnt/backuppc/pc/abc.def.ghi/1989/refCnt/poolCnt.1.16
>> /mnt/backuppc/cpool/5c/c8/5cc9373a32e06baaa308a7b341db5ac9
>> /mnt/backuppc/cpool/b2/62/b3629c46481cb038682aea248c45b89f
>> /mnt/backuppc/cpool/20/c6/21c61013d40e644af734e28459df0a1a
>> /mnt/backuppc/cpool/8a/f8/8af935bc53f7199ed75a5695bfd57f26
>> 
>> FYI: The most recent backup from host abc.def.ghi is 2291, so 1989 is
>> quite far in the past.
>> 
>> How should I proceed when I have a list of broken files?
>> Move them out from cpool and hope they will be re-synced by the next
>> (full?) backup?
>> 
>> Thanks,
>> Raoul
>> 
>>> Craig
>>> 
>>> On Sun, Aug 23, 2020 at 6:45 AM Guillermo Rozas 
>>> <[email protected]> wrote:
>>> 
>>> Hi Raoul,
>>> 
>>> are you using BackupPC v4? If yes, you can use a modification of the 
>>> script I posted here: 
>>> https://sourceforge.net/p/backuppc/mailman/message/37032497/
>>> 
>>> In the latest version (4.4.0) you also have the config option 
>>> $Conf{PoolNightlyDigestCheckPercent}, which checks the md5 digest of 
>>> this fraction of the pool files each night. You can probably set it 
>>> to 1 and wait a night for it to run.
>>> 
>>> Regards,
>>> Guillermo
>>> 
>>> On Sun, Aug 23, 2020 at 5:38 AM Raoul Bhatia <[email protected]> wrote: 
>>> Hi,
>>> 
>>> related to my previous email, it seems that the cause of my issues 
>>> was a
>>> file system corruption after a "power cut".
>>> 
>>> I managed to recover (most of?) the data and would now like to do a
>>> thorough check of the data.
>>> 
>>> Is there any way to "fully verify" the integrity of my backuppc
>>> installation, ideally in a nondestructive way ;-)
>>> 
>>> Thanks,
>>> Raoul
>>> 
>>> PS. My backuppc process is stopped.
>>> --
>>> DI (FH) Raoul Bhatia MSc
>>> E-Mail. [email protected]
>>> Tel. +43 699 10132530
> 
> 
> 
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-- 
DI (FH) Raoul Bhatia MSc
E-Mail. [email protected]
Tel. +43 699 10132530


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