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Re: trying to avoid a lengthy quotacheck by deleting all quota data

To: xfs@xxxxxxxxxxx
Subject: Re: trying to avoid a lengthy quotacheck by deleting all quota data
From: Harry <harry@xxxxxxxxxxxxxxxxxx>
Date: Thu, 05 Mar 2015 13:15:19 +0000
Cc: "developers@xxxxxxxxxxxxxxxxxx" <developers@xxxxxxxxxxxxxxxxxx>
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Update -- so far, we've not managed to gain any confidence that we'll ever be able to re-mount that disk. The general consensus seems to be to fish all the data off the disk using rsync, and then move off XFS to ext4.

Not a very helpful message for y'all to hear, I know.  But if it's any help in prioritising your future work, i think the dealbreaker for us was the inescapable quotacheck on mount, which means that any time a fileserver goes down unexpectedly, we have an unavoidable, indeterminate-but-long period of downtime...

hp

On 26/02/15 13:07, Harry wrote:
Thanks Dave,

* The main filesystem is currently online and seems ok, but quotas are not active.
* We want to estimate how long the quotacheck will take when we reboot/remount
* We're even a bit worried the disk might be in a broken state, such that the quotacheck won't actually complete successfully at all.

A brief description of our setup:
- we're on AWS
- using mdadm to make a raid array out of 8x 200GB SSD EBS drives (and lvm)
- we're using DRBD to make a live backup of all writes to another instance with a similar raid array

We're not doing our experiments on our live system.  Instead, we're using the drives from the DRBD target system.  We take DRBD offline, so it's no longer writing, then we take snapshots of the drives, then remount those elsewhere so we can experiment without disturbing the live system.

We've managed to mount the backup drives ok, with the 'noquota' option.  Files look ok.  But, so far, we haven't been able to get a quotacheck to complete.  We've waited 12 hours+. Do you think it's possible DRBD is giving us copies of the live disks that are inconsistent somehow?

How can we reassure ourselves that this live disk *will* mount successfully if we reboot the machine, and can we estimate how long it will take?
mount | grep log_storage
/dev/drbd0 on /mnt/log_storage type xfs (rw,prjquota,allocsize=64k,_netdev)

df -i /mnt/log_storage/
Filesystem        Inodes    IUsed     IFree IUse% Mounted on
/dev/drbd0     938210704 72929413 865281291    8% /mnt/log_storage

df -h /mnt/log_storage/
Filesystem      Size  Used Avail Use% Mounted on
/dev/drbd0      1.6T  1.4T  207G  88% /mnt/log_storage

xfs_info /mnt/log_storage/
<lots of errors re: cannot find mount point path `xyz`>
meta-data="" isize=256    agcount=64, agsize=6553600 blks
         =                       sectsz=512   attr=2
data     =                       bsize=4096   blocks=418906112, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0
log      =internal               bsize=4096   blocks=12800, version=2
         =                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0

The missing paths errors are, I think, from folders we've deleted but not yet removed from the projid/projects folders. I *think* they're a red herring here.

We've also tried running xfs_repair on the backup drives.  It takes about 3 hours, and shows a lot of errors about incorrect directory flags on inodes.  here's one from the bottom of the log of a recent attempt:

directory flags set on non-directory inode 268702898

rgds,
Confused in London.



On 24/02/15 21:59, Dave Chinner wrote:
On Tue, Feb 24, 2015 at 03:15:26PM +0000, Harry wrote:
Hi there,

We've got a moderately large disk (~2TB) into an inconsistent state,
such that it's going to want a quotacheck the next time we mount it
(it's currently mounted with quota accounting inactive).  Our tests
suggest this is going to take several hours, and cause an outage we
can't afford.
What tests are you performing to suggest a quotacheck of a small
filesystem will take hours? (yes, 2TB is a *small* filesystem).

(xfs_info, df -i, df -h, storage hardware, etc are all relevant
here).

We're wondering whether there's a 'nuke the site from orbit' option
that will let us avoid it.  The plan would be to:
- switch off quotas and delete them completely, using the commands:
  -- disable
  -- off
  -- remove
- remount the drive with -o prjquota, hoping that there will not be
a quotacheck, because we've deleted all the old quota data
Mounting with a quota enabled *forces* a quota check if quotas
aren't currently enabled. You cannot avoid it; it's the way quota
consistency is created.

- run a script gradually restore all the quotas, one by one and in
good time, from our own external backups (we've got the quotas in a
database basically).
Can't be done - quotas need to be consistent with what is currently
on disk, not what you have in a backup somewhere.

So the questions are:
- is there a way to remove all quota information from a mounted drive?
(the current mount status seems to be that it tried to mount it with
mount with quotas on and turn them off via xfs_quota,i or mount
without quota options at all. Then run the remove command in
xfs_quota.

-o prjquota but that quota accounting is *not* active)
Not possible.

- will it work and let us remount the drive with -o prjquota without
causing a quotacheck?
No.

Cheers,

Dave.

Rgds,
Harry + the PythonAnywhere team.

-- 
Harry Percival
Developer
harry@xxxxxxxxxxxxxxxxxx

PythonAnywhere - a fully browser-based Python development and hosting environment
<http://www.pythonanywhere.com/>

PythonAnywhere LLP
17a Clerkenwell Road, London EC1M 5RD, UK
VAT No.: GB 893 5643 79
Registered in England and Wales as company number OC378414.
Registered address: 28 Ely Place, 3rd Floor, London EC1N 6TD, UK

Rgds,
Harry + the PythonAnywhere team.

-- 
Harry Percival
Developer
harry@xxxxxxxxxxxxxxxxxx

PythonAnywhere - a fully browser-based Python development and hosting environment
<http://www.pythonanywhere.com/>

PythonAnywhere LLP
17a Clerkenwell Road, London EC1M 5RD, UK
VAT No.: GB 893 5643 79
Registered in England and Wales as company number OC378414.
Registered address: 28 Ely Place, 3rd Floor, London EC1N 6TD, UK
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