On 2016-09-29 9:32 am, Dean E. Weimer wrote:> I discovered, unfortunately by deleting a jail by accident, that my
> backup process isn't working. At least it was only the operating
> system part of the jail, I still have all the data so I just need to
> reinstall the operating system. While the ports are in the process of
> building I started to investigate the cause, because the backup logs
> report everything was fine.
>
> I have a custom pre-backup script I wrote that takes snapshots of my
> ZFS datasets, and then mounts those under /mnt/backup with nullfs
> mount points to the .zfs/snapshot/.. directories then I back them up
> rather than the live file system, allowing me to stop some services
> that don't restore from a running state correctly and then restart
> after the snapshot so downtime is only a couple of minutes instead of
> full length of backups.
>
> It appeared to be running perfectly, without errors, but apparently
> the script isn't reporting some nullfs mount failures, so why are the
> failing, turns out it thinks the file name is too long? but looking at
> the mount(2) man page it states this:
>
> [ENAMETOOLONG] A component of a pathname exceeded 255 characters,
> or
> the entire length of a path name exceeded 1023
> characters.
>
> I can see that at some point under this, I may reach that 1023 limit,
> but what of the total 71 characters in this path has a problem?
>
> /jails/unifi/ROOT/.zfs/snapshot/11.0-RELEASE-r306379-2016.09.28--bsnap
>
> root at freebsd:/jails/unifi/ROOT/.zfs/snapshot # ls
> ls: 11.0-RELEASE-r306379-2016.09.28--bsnap: File name too long
>
> I thought, maybe its a ZFS specific error, and ran across this:
> http://lists.freebsd.org/pipermail/freebsd-fs/2010-March/007964.html
>
> [..snip..]
> From looking at the code, I think you hitting this limit:
>
> /*
> * Be ultra-paranoid about making sure the type and fspath
> * variables will fit in our mp buffers, including the
> * terminating NUL.
> */
> if (strlen(fstype) >= MFSNAMELEN || strlen(fspath) >= MNAMELEN)
> return (ENAMETOOLONG);
>
> in vfs_domount() or vfs_donmount().
>
> This is FreeBSD limit caused by statfs structure:
>
> /*
> * filesystem statistics
> */
> [...]
> #define MNAMELEN 88 /* size of on/from name bufs */
> [...]
> struct statfs {
> [...]
> char f_mntfromname[MNAMELEN];/* mounted filesystem */
> char f_mntonname[MNAMELEN]; /* directory on which mounted */
> };
>
> When you list .zfs/snapshot/ directory (especially with -l option) ZFS
> mounts snapshots on lookup and this is this mount that fails.
> [..snip..]
>
> I can seemingly due anything else with the snapshot, clone, send,
> receive its just that I am unable to access the files on it through
> .zfs/snapshot/..
>
> I am trying to find what the limit is here from this, because this one
> here works.
>
>
/jails/webmail/usr-local-subversion/.zfs/snapshot/usr-local-subversion--bsnap
>
> its longer in total length than most of the ones that are failing.
>
> /jails/unifi/ROOT/.zfs/snapshot/11.0-RELEASE-r306379-2016.09.28--bsnap
>
> So it appears that its in the name, and not the mount point.
>
> this one works as well, which is my ZFS boot environment on the main
> system
> zraid/ROOT/11.0-RELEASE-r306379-2016.09.28
> snapshot is /.zfs/snapshot/11.0-RELEASE-r306379-2016.09.28--bsnap
>
> So its not just the last component of the zfs dataset name, which is
> in this case the same.
>
> I am trying to wrap my head around this and find where the limit is so
> I can adjust my naming conventions used and actually get backups of
> all of my data. Turns out all of my jail operating system paths aren't
> being backed up, fortunately at least all of the data file systems for
> the jails are.
I found a solution, I was naming the snapshots with the dataset name,
which I think was causing the issue.
The following didn't seem to long to be an issue
/jails/unifi/ROOT/.zfs/snapshot/11.0-RELEASE-r306379-2016.09.28--bsnap
But apparently the snapshot name was
zraid/jails/unifi/11.0-RELEASE-r306379-2016.09.28 at
11.0-RELEASE-r306379-2016.09.28--bsnap
Still not sure how it adds up to too long, both full paths together
aren't over 255, at 160, but apparently something else is added in
there. I was able to easily modify my backup script to not include the
last part of the dataset in the snapshot name and simply use -bsnap-, as
the name. it appears to avoid all the issues, and my backups from last
night include all the files.
/jails/unifi/ROOT/.zfs/snapshot/-bsnap-
zraid/jails/unifi/11.0-RELEASE-r306379-2016.09.28 at -bsnap-
The total path now only adds up to 98, I haven't done any testing yet to
find out where the limit is hit, The longest combination of these I had
last night would have added up to 135, and that worked
--
Thanks,
Dean E. Weimer
http://www.dweimer.net/