[Gluster-users] Does replace-brick migrate data?
Ravishankar N
ravishankar at redhat.com
Mon Jun 3 16:40:00 UTC 2019
On 01/06/19 9:37 PM, Alan Orth wrote:
> Dear Ravi,
>
> The .glusterfs hardlinks/symlinks should be fine. I'm not sure how I
> could verify them for six bricks and millions of files, though... :\
Hi Alan,
The reason I asked this is because you had mentioned in one of your
earlier emails that when you moved content from the old brick to the new
one, you had skipped the .glusterfs directory. So I was assuming that
when you added back this new brick to the cluster, it might have been
missing the .glusterfs entries. If that is the cae, one way to verify
could be to check using a script if all files on the brick have a
link-count of at least 2 and all dirs have valid symlinks inside
.glusterfs pointing to themselves.
>
> I had a small success in fixing some issues with duplicated files on
> the FUSE mount point yesterday. I read quite a bit about the elastic
> hashing algorithm that determines which files get placed on which
> bricks based on the hash of their filename and the
> trusted.glusterfs.dht xattr on brick directories (thanks to Joe
> Julian's blog post and Python script for showing how it works¹). With
> that knowledge I looked closer at one of the files that was appearing
> as duplicated on the FUSE mount and found that it was also duplicated
> on more than `replica 2` bricks. For this particular file I found two
> "real" files and several zero-size files with
> trusted.glusterfs.dht.linkto xattrs. Neither of the "real" files were
> on the correct brick as far as the DHT layout is concerned, so I
> copied one of them to the correct brick, deleted the others and their
> hard links, and did a `stat` on the file from the FUSE mount point and
> it fixed itself. Yay!
>
> Could this have been caused by a replace-brick that got interrupted
> and didn't finish re-labeling the xattrs?
No, replace-brick only initiates AFR self-heal, which just copies the
contents from the other brick(s) of the *same* replica pair into the
replaced brick. The link-to files are created by DHT when you rename a
file from the client. If the new name hashes to a different brick, DHT
does not move the entire file there. It instead creates the link-to file
(the one with the dht.linkto xattrs) on the hashed subvol. The value of
this xattr points to the brick where the actual data is there (`getfattr
-e text` to see it for yourself). Perhaps you had attempted a rebalance
or remove-brick earlier and interrupted that?
> Should I be thinking of some heuristics to identify and fix these
> issues with a script (incorrect brick placement), or is this something
> a fix layout or repeated volume heals can fix? I've already completed
> a whole heal on this particular volume this week and it did heal about
> 1,000,000 files (mostly data and metadata, but about 20,000 entry
> heals as well).
>
Maybe you should let the AFR self-heals complete first and then attempt
a full rebalance to take care of the dht link-to files. But if the
files are in millions, it could take quite some time to complete.
Regards,
Ravi
> Thanks for your support,
>
> ¹ https://joejulian.name/post/dht-misses-are-expensive/
>
> On Fri, May 31, 2019 at 7:57 AM Ravishankar N <ravishankar at redhat.com
> <mailto:ravishankar at redhat.com>> wrote:
>
>
> On 31/05/19 3:20 AM, Alan Orth wrote:
>> Dear Ravi,
>>
>> I spent a bit of time inspecting the xattrs on some files and
>> directories on a few bricks for this volume and it looks a bit
>> messy. Even if I could make sense of it for a few and potentially
>> heal them manually, there are millions of files and directories
>> in total so that's definitely not a scalable solution. After a
>> few missteps with `replace-brick ... commit force` in the last
>> week—one of which on a brick that was dead/offline—as well as
>> some premature `remove-brick` commands, I'm unsure how how to
>> proceed and I'm getting demotivated. It's scary how quickly
>> things get out of hand in distributed systems...
> Hi Alan,
> The one good thing about gluster is it that the data is always
> available directly on the backed bricks even if your volume has
> inconsistencies at the gluster level. So theoretically, if your
> cluster is FUBAR, you could just create a new volume and copy all
> data onto it via its mount from the old volume's bricks.
>>
>> I had hoped that bringing the old brick back up would help, but
>> by the time I added it again a few days had passed and all the
>> brick-id's had changed due to the replace/remove brick commands,
>> not to mention that the trusted.afr.$volume-client-xx values were
>> now probably pointing to the wrong bricks (?).
>>
>> Anyways, a few hours ago I started a full heal on the volume and
>> I see that there is a sustained 100MiB/sec of network traffic
>> going from the old brick's host to the new one. The completed
>> heals reported in the logs look promising too:
>>
>> Old brick host:
>>
>> # grep '2019-05-30' /var/log/glusterfs/glustershd.log | grep -o
>> -E 'Completed (data|metadata|entry) selfheal' | sort | uniq -c
>> 281614 Completed data selfheal
>> 84 Completed entry selfheal
>> 299648 Completed metadata selfheal
>>
>> New brick host:
>>
>> # grep '2019-05-30' /var/log/glusterfs/glustershd.log | grep -o
>> -E 'Completed (data|metadata|entry) selfheal' | sort | uniq -c
>> 198256 Completed data selfheal
>> 16829 Completed entry selfheal
>> 229664 Completed metadata selfheal
>>
>> So that's good I guess, though I have no idea how long it will
>> take or if it will fix the "missing files" issue on the FUSE
>> mount. I've increased cluster.shd-max-threads to 8 to hopefully
>> speed up the heal process.
> The afr xattrs should not cause files to disappear from mount. If
> the xattr names do not match what each AFR subvol expects (for eg.
> in a replica 2 volume, trusted.afr.*-client-{0,1} for 1st subvol,
> client-{2,3} for 2nd subvol and so on - ) for its children then it
> won't heal the data, that is all. But in your case I see some
> inconsistencies like one brick having the actual file
> (licenseserver.cfg) and the other having a linkto file (the one
> with thedht.linkto xattr) /in the same replica pair/.
>>
>> I'd be happy for any advice or pointers,
>
> Did you check if the .glusterfs hardlinks/symlinks exist and are
> in order for all bricks?
>
> -Ravi
>
>>
>> On Wed, May 29, 2019 at 5:20 PM Alan Orth <alan.orth at gmail.com
>> <mailto:alan.orth at gmail.com>> wrote:
>>
>> Dear Ravi,
>>
>> Thank you for the link to the blog post series—it is very
>> informative and current! If I understand your blog post
>> correctly then I think the answer to your previous question
>> about pending AFRs is: no, there are no pending AFRs. I have
>> identified one file that is a good test case to try to
>> understand what happened after I issued the `gluster volume
>> replace-brick ... commit force` a few days ago and then added
>> the same original brick back to the volume later. This is the
>> current state of the replica 2 distribute/replicate volume:
>>
>> [root at wingu0 ~]# gluster volume info apps
>>
>> Volume Name: apps
>> Type: Distributed-Replicate
>> Volume ID: f118d2da-79df-4ee1-919d-53884cd34eda
>> Status: Started
>> Snapshot Count: 0
>> Number of Bricks: 3 x 2 = 6
>> Transport-type: tcp
>> Bricks:
>> Brick1: wingu3:/mnt/gluster/apps
>> Brick2: wingu4:/mnt/gluster/apps
>> Brick3: wingu05:/data/glusterfs/sdb/apps
>> Brick4: wingu06:/data/glusterfs/sdb/apps
>> Brick5: wingu0:/mnt/gluster/apps
>> Brick6: wingu05:/data/glusterfs/sdc/apps
>> Options Reconfigured:
>> diagnostics.client-log-level: DEBUG
>> storage.health-check-interval: 10
>> nfs.disable: on
>>
>> I checked the xattrs of one file that is missing from the
>> volume's FUSE mount (though I can read it if I access its
>> full path explicitly), but is present in several of the
>> volume's bricks (some with full size, others empty):
>>
>> [root at wingu0 ~]# getfattr -d -m. -e hex
>> /mnt/gluster/apps/clcgenomics/clclicsrv/licenseserver.cfg
>>
>> getfattr: Removing leading '/' from absolute path names #
>> file:
>> mnt/gluster/apps/clcgenomics/clclicsrv/licenseserver.cfg
>> security.selinux=0x73797374656d5f753a6f626a6563745f723a756e6c6162656c65645f743a733000
>> trusted.afr.apps-client-3=0x000000000000000000000000
>> trusted.afr.apps-client-5=0x000000000000000000000000
>> trusted.afr.dirty=0x000000000000000000000000
>> trusted.bit-rot.version=0x0200000000000000585a396f00046e15
>> trusted.gfid=0x878003a2fb5243b6a0d14d2f8b4306bd [root at wingu05
>> ~]# getfattr -d -m. -e hex
>> /data/glusterfs/sdb/apps/clcgenomics/clclicsrv/licenseserver.cfg
>> getfattr: Removing leading '/' from absolute path names #
>> file:
>> data/glusterfs/sdb/apps/clcgenomics/clclicsrv/licenseserver.cfg
>> security.selinux=0x73797374656d5f753a6f626a6563745f723a756e6c6162656c65645f743a733000
>> trusted.gfid=0x878003a2fb5243b6a0d14d2f8b4306bd
>> trusted.gfid2path.82586deefbc539c3=0x34666437323861612d356462392d343836382d616232662d6564393031636566333561392f6c6963656e73657365727665722e636667
>> trusted.glusterfs.dht.linkto=0x617070732d7265706c69636174652d3200
>> [root at wingu05 ~]# getfattr -d -m. -e hex
>> /data/glusterfs/sdc/apps/clcgenomics/clclicsrv/licenseserver.cfg
>> getfattr: Removing leading '/' from absolute path names #
>> file:
>> data/glusterfs/sdc/apps/clcgenomics/clclicsrv/licenseserver.cfg
>> security.selinux=0x73797374656d5f753a6f626a6563745f723a756e6c6162656c65645f743a733000
>> trusted.gfid=0x878003a2fb5243b6a0d14d2f8b4306bd
>> trusted.gfid2path.82586deefbc539c3=0x34666437323861612d356462392d343836382d616232662d6564393031636566333561392f6c6963656e73657365727665722e636667
>> [root at wingu06 ~]# getfattr -d -m. -e hex
>> /data/glusterfs/sdb/apps/clcgenomics/clclicsrv/licenseserver.cfg
>> getfattr: Removing leading '/' from absolute path names #
>> file:
>> data/glusterfs/sdb/apps/clcgenomics/clclicsrv/licenseserver.cfg
>> security.selinux=0x73797374656d5f753a6f626a6563745f723a756e6c6162656c65645f743a733000
>> trusted.gfid=0x878003a2fb5243b6a0d14d2f8b4306bd
>> trusted.gfid2path.82586deefbc539c3=0x34666437323861612d356462392d343836382d616232662d6564393031636566333561392f6c6963656e73657365727665722e636667
>> trusted.glusterfs.dht.linkto=0x617070732d7265706c69636174652d3200
>>
>> According to the trusted.afr.apps-client-xxxattrs this
>> particular file should be on bricks with id "apps-client-3"
>> and "apps-client-5". It took me a few hours to realize that
>> the brick-id values are recorded in the volume's volfiles in
>> /var/lib/glusterd/vols/apps/bricks. After comparing those
>> brick-id values with a volfile backup from before the
>> replace-brick, I realized that the files are simply on the
>> wrong brick now as far as Gluster is concerned. This
>> particular file is now on the brick for "apps-client-4". As
>> an experiment I copied this one file to the two bricks listed
>> in the xattrs and I was then able to see the file from the
>> FUSE mount (yay!).
>>
>> Other than replacing the brick, removing it, and then adding
>> the old brick on the original server back, there has been no
>> change in the data this entire time. Can I change the brick
>> IDs in the volfiles so they reflect where the data actually
>> is? Or perhaps script something to reset all the xattrs on
>> the files/directories to point to the correct bricks?
>>
>> Thank you for any help or pointers,
>>
>> On Wed, May 29, 2019 at 7:24 AM Ravishankar N
>> <ravishankar at redhat.com <mailto:ravishankar at redhat.com>> wrote:
>>
>>
>> On 29/05/19 9:50 AM, Ravishankar N wrote:
>>>
>>>
>>> On 29/05/19 3:59 AM, Alan Orth wrote:
>>>> Dear Ravishankar,
>>>>
>>>> I'm not sure if Brick4 had pending AFRs because I don't
>>>> know what that means and it's been a few days so I am
>>>> not sure I would be able to find that information.
>>> When you find some time, have a look at a blog
>>> <http://wp.me/peiBB-6b> series I wrote about AFR- I've
>>> tried to explain what one needs to know to debug
>>> replication related issues in it.
>>
>> Made a typo error. The URL for the blog is
>> https://wp.me/peiBB-6b
>>
>> -Ravi
>>
>>>>
>>>> Anyways, after wasting a few days rsyncing the old
>>>> brick to a new host I decided to just try to add the
>>>> old brick back into the volume instead of bringing it
>>>> up on the new host. I created a new brick directory on
>>>> the old host, moved the old brick's contents into that
>>>> new directory (minus the .glusterfs directory), added
>>>> the new brick to the volume, and then did Vlad's
>>>> find/stat trick¹ from the brick to the FUSE mount point.
>>>>
>>>> The interesting problem I have now is that some files
>>>> don't appear in the FUSE mount's directory listings,
>>>> but I can actually list them directly and even read
>>>> them. What could cause that?
>>> Not sure, too many variables in the hacks that you did
>>> to take a guess. You can check if the contents of the
>>> .glusterfs folder are in order on the new brick (example
>>> hardlink for files and symlinks for directories are
>>> present etc.) .
>>> Regards,
>>> Ravi
>>>>
>>>> Thanks,
>>>>
>>>> ¹
>>>> https://lists.gluster.org/pipermail/gluster-users/2018-February/033584.html
>>>>
>>>> On Fri, May 24, 2019 at 4:59 PM Ravishankar N
>>>> <ravishankar at redhat.com
>>>> <mailto:ravishankar at redhat.com>> wrote:
>>>>
>>>>
>>>> On 23/05/19 2:40 AM, Alan Orth wrote:
>>>>> Dear list,
>>>>>
>>>>> I seem to have gotten into a tricky situation.
>>>>> Today I brought up a shiny new server with new
>>>>> disk arrays and attempted to replace one brick of
>>>>> a replica 2 distribute/replicate volume on an
>>>>> older server using the `replace-brick` command:
>>>>>
>>>>> # gluster volume replace-brick homes
>>>>> wingu0:/mnt/gluster/homes
>>>>> wingu06:/data/glusterfs/sdb/homes commit force
>>>>>
>>>>> The command was successful and I see the new brick
>>>>> in the output of `gluster volume info`. The
>>>>> problem is that Gluster doesn't seem to be
>>>>> migrating the data,
>>>>
>>>> `replace-brick` definitely must heal (not migrate)
>>>> the data. In your case, data must have been healed
>>>> from Brick-4 to the replaced Brick-3. Are there any
>>>> errors in the self-heal daemon logs of Brick-4's
>>>> node? Does Brick-4 have pending AFR xattrs blaming
>>>> Brick-3? The doc is a bit out of date.
>>>> replace-brick command internally does all the
>>>> setfattr steps that are mentioned in the doc.
>>>>
>>>> -Ravi
>>>>
>>>>
>>>>> and now the original brick that I replaced is no
>>>>> longer part of the volume (and a few terabytes of
>>>>> data are just sitting on the old brick):
>>>>>
>>>>> # gluster volume info homes | grep -E "Brick[0-9]:"
>>>>> Brick1: wingu4:/mnt/gluster/homes
>>>>> Brick2: wingu3:/mnt/gluster/homes
>>>>> Brick3: wingu06:/data/glusterfs/sdb/homes
>>>>> Brick4: wingu05:/data/glusterfs/sdb/homes
>>>>> Brick5: wingu05:/data/glusterfs/sdc/homes
>>>>> Brick6: wingu06:/data/glusterfs/sdc/homes
>>>>>
>>>>> I see the Gluster docs have a more complicated
>>>>> procedure for replacing bricks that involves
>>>>> getfattr/setfattr¹. How can I tell Gluster about
>>>>> the old brick? I see that I have a backup of the
>>>>> old volfile thanks to yum's rpmsave function if
>>>>> that helps.
>>>>>
>>>>> We are using Gluster 5.6 on CentOS 7. Thank you
>>>>> for any advice you can give.
>>>>>
>>>>> ¹
>>>>> https://docs.gluster.org/en/latest/Administrator%20Guide/Managing%20Volumes/#replace-faulty-brick
>>>>>
>>>>> --
>>>>> Alan Orth
>>>>> alan.orth at gmail.com <mailto:alan.orth at gmail.com>
>>>>> https://picturingjordan.com
>>>>> https://englishbulgaria.net
>>>>> https://mjanja.ch
>>>>> "In heaven all the interesting people are
>>>>> missing." ―Friedrich Nietzsche
>>>>>
>>>>> _______________________________________________
>>>>> Gluster-users mailing list
>>>>> Gluster-users at gluster.org <mailto:Gluster-users at gluster.org>
>>>>> https://lists.gluster.org/mailman/listinfo/gluster-users
>>>>
>>>>
>>>>
>>>> --
>>>> Alan Orth
>>>> alan.orth at gmail.com <mailto:alan.orth at gmail.com>
>>>> https://picturingjordan.com
>>>> https://englishbulgaria.net
>>>> https://mjanja.ch
>>>> "In heaven all the interesting people are missing."
>>>> ―Friedrich Nietzsche
>>>
>>> _______________________________________________
>>> Gluster-users mailing list
>>> Gluster-users at gluster.org <mailto:Gluster-users at gluster.org>
>>> https://lists.gluster.org/mailman/listinfo/gluster-users
>>
>>
>>
>> --
>> Alan Orth
>> alan.orth at gmail.com <mailto:alan.orth at gmail.com>
>> https://picturingjordan.com
>> https://englishbulgaria.net
>> https://mjanja.ch
>> "In heaven all the interesting people are missing."
>> ―Friedrich Nietzsche
>>
>>
>>
>> --
>> Alan Orth
>> alan.orth at gmail.com <mailto:alan.orth at gmail.com>
>> https://picturingjordan.com
>> https://englishbulgaria.net
>> https://mjanja.ch
>> "In heaven all the interesting people are missing." ―Friedrich
>> Nietzsche
>
>
>
> --
> Alan Orth
> alan.orth at gmail.com <mailto:alan.orth at gmail.com>
> https://picturingjordan.com
> https://englishbulgaria.net
> https://mjanja.ch
> "In heaven all the interesting people are missing." ―Friedrich Nietzsche
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