xfs fstrim and quota

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

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.

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

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

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

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