Re: xfs fstrim and quota

Re: xfs fstrim and quota

[michael.arndt]

Hello *

Will fstrim operations for a thin provisioning storage and xfs quota 
conflict with each other ?

If i understand fstrim code correctly, in case of xfs / thin 
provisioning  storage it tells xfs to release unused blocks.

I have read indications that blocks are marked to the underlying storage 
as freed by zeroing them out.

Is the "write zeros" correct information, or will be commands like scsi 
unmap or FITRIM be sent to the storage ?

I found many exact references to fstrim on SSD, but no technical 
description on which operation is implemented for thin provisioning 
storages.

TIA
Micha

Re: xfs fstrim and quota

[Brian Foster]

On Tue, Apr 24, 2018 at 10:28:34AM +0200, michael.arndt@berlin.de wrote:
> Hello *
> 
> Will fstrim operations for a thin provisioning storage and xfs quota
> conflict with each other ?
> 

How so? fstrim should basically inform the underlying device of blocks
in the filesystem that are free. Free blocks in the fs aren't accounted
to any quota by definition, so there shouldn't be a conflict.

> If i understand fstrim code correctly, in case of xfs / thin provisioning
> storage it tells xfs to release unused blocks.
> 

Right... so an underlying thin block device can release blocks that are
unused in the fs.

> I have read indications that blocks are marked to the underlying storage as
> freed by zeroing them out.
> 
> Is the "write zeros" correct information, or will be commands like scsi
> unmap or FITRIM be sent to the storage ?
> 

The fs invokes the block layer discard mechanism. I can't really speak
to how this translates into device commands. My understanding is that a
dm-thin device would/could act on this to release associated blocks to
the pool, otherwise the behavior may depend on the physical
characteristics of the underlying device (i.e., SSD, non-dm thin
devices, etc.), supported commands or whatnot. Perhaps somebody else can
chime in on that or otherwise this might be a better question for the
block layer folks.

Brian

> I found many exact references to fstrim on SSD, but no technical description
> on which operation is implemented for thin provisioning storages.
> 
> TIA
> Micha
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xfs remove / unlink extremely slow ?

[Michael Arndt]

Hello *,

Problem: /bin/rm extremely slow on a major xfs (SSD based) HPC Storage
               slow == 90 seconds for unlink of an empty file without any extents
               strace says: time completely used for unlink call

Question; Is there any issue resolution ?
Information re XFS Version and OS at end of this Post

Example of issue:

[root@atgrzsl3150 DOM_0]# xfs_bmap -a .AN_720.0000122.fl3step_0.lock 
.AN_720.0000122.fl3step_0.lock: no extents

[root@atgrzsl3150 DOM_0]# ls -laFtr .AN_720.0000122.fl3step_0.lock 
-rw-rw-r-- 1 user group 0 Oct 22 14:14 .AN_720.0000122.fl3step_0.lock

strace -T -tt /bin/rm .AN_720.0000122.fl3step_0.lock 
11:41:11.621005 execve("/bin/rm", ["/bin/rm", ".AN_720.0000122.fl3step_0.lock"], [/* 31 vars */]) = 0 <0.000169>
11:41:11.621312 brk(NULL)               = 0x6f5000 <0.000023>
11:41:11.621378 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f4d96017000 <0.000058>
…….
11:41:11.622485 newfstatat(AT_FDCWD, ".AN_720.0000122.fl3step_0.lock", {st_mode=S_IFREG|0664, st_size=0, ...}, AT_SYMLINK_NOFOLLOW) = 0 <0.000009>
11:41:11.622522 geteuid()               = 0 <0.000009>
-> 11:41:11.622546 unlinkat(AT_FDCWD, ".AN_720.0000122.fl3step_0.lock", 0) = 0 <89.612833>
-> 11:42:41.235428 lseek(0, 0, SEEK_CUR)   = -1 ESPIPE (Illegal seek) <0.000065>
11:42:41.235548 close(0)                = 0 <0.000052>
11:42:41.235689 close(1)                = 0 <0.000011>
11:42:41.235738 close(2)                = 0 <0.000055>
11:42:41.235830 exit_group(0)           = ?
11:42:41.235941 +++ exited with 0 +++

xfs_info /dev/mapper/vg_calc2-calc2
meta-data=/dev/mapper/vg_calc2-calc2 isize=512    agcount=50, agsize=268435448 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=0 spinodes=0
data     =                       bsize=4096   blocks=13421711360, imaxpct=20
         =                       sunit=8      swidth=40 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
log      =internal               bsize=4096   blocks=521728, version=2
         =                       sectsz=512   sunit=8 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0


Issue on:

xfsprogs-4.5.0-18.el7.x86_64
xfsdump-3.1.7-1.el7.x86_64
Red Hat Enterprise Linux Server release 7.4 (Maipo)
 df -kh .
Filesystem                  Size  Used Avail Use% Mounted on
/dev/mapper/vg_calc2        50T   20T   31T  40% /calc2

Layers: 

SSD based commercial Storage exports many small LUN’s -> LUN#s striped via LVM2 for speed, xfs with default opts on top of LVM
Currently no discard Option for mount and no fstrim manually called

Mount Options used
/dev/mapper/vg_calc2-calc2 /calc2 xfs noatime,delaylog,nobarrier,nodiratime,logbsize=256k,logbufs=8 0 0 


thanks for any tip / hint / question
Micha

Re: xfs fstrim and quota

[Eric Sandeen]

On 4/24/18 2:28 AM, michael.arndt@berlin.de wrote:
> Hello *
> 
> Will fstrim operations for a thin provisioning storage and xfs quota conflict with each other ?
> 
> If i understand fstrim code correctly, in case of xfs / thin provisioning  storage it tells xfs to release unused blocks.
> 
> I have read indications that blocks are marked to the underlying storage as freed by zeroing them out.

Brian addressed most of this, I think, but the short answer is that no, fstrim
will in no way affect xfs quota.  Everything happening as a result of fstrim
happens well below what the quota subsystem even knows about.  Even if discard
happens via WRITE_SAME, that's not anything quota is aware of.

Short answer is: There is no conflict.

Thanks,
-Eric
 
> Is the "write zeros" correct information, or will be commands like scsi unmap or FITRIM be sent to the storage ?
> 
> I found many exact references to fstrim on SSD, but no technical description on which operation is implemented for thin provisioning storages.
> 
> TIA
> Micha