Is XFS suitable for 350 million files on 20TB storage?

[Brian Foster]

On Fri, Sep 05, 2014 at 02:40:32PM +0200, Stefan Priebe - Profihost AG wrote:
> 
> Am 05.09.2014 um 14:30 schrieb Brian Foster:
> > On Fri, Sep 05, 2014 at 11:47:29AM +0200, Stefan Priebe - Profihost AG wrote:
> >> Hi,
> >>
> >> i have a backup system running 20TB of storage having 350 million files.
> >> This was working fine for month.
> >>
> >> But now the free space is so heavily fragmented that i only see the
> >> kworker with 4x 100% CPU and write speed beeing very slow. 15TB of the
> >> 20TB are in use.
> >>
> >> Overall files are 350 Million - all in different directories. Max 5000
> >> per dir.
> >>
> >> Kernel is 3.10.53 and mount options are:
> >> noatime,nodiratime,attr2,inode64,logbufs=8,logbsize=256k,noquota
> >>
> >> # xfs_db -r -c freesp /dev/sda1
> >>    from      to extents  blocks    pct
> >>       1       1 29484138 29484138   2,16
> >>       2       3 16930134 39834672   2,92
> >>       4       7 16169985 87877159   6,45
> >>       8      15 78202543 999838327  73,41
> >>      16      31 3562456 83746085   6,15
> >>      32      63 2370812 102124143   7,50
> >>      64     127  280885 18929867   1,39
> >>     256     511       2     827   0,00
> >>     512    1023      65   35092   0,00
> >>    2048    4095       2    6561   0,00
> >>   16384   32767       1   23951   0,00
> >>
> >> Is there anything i can optimize? Or is it just a bad idea to do this
> >> with XFS? Any other options? Maybe rsync options like --inplace /
> >> --no-whole-file?
> >>
> > 
> > It's probably a good idea to include more information about your fs:
> > 
> > http://xfs.org/index.php/XFS_FAQ#Q:_What_information_should_I_include_when_reporting_a_problem.3F
> 
> Generally sure but the problem itself is clear. If you look at the free
> space allocation you see that free space is heavily fragmented.
> 
> But here you go:
> - 3.10.53 vanilla
> - xfs_repair version 3.1.11
> - 16 cores
> - /dev/sda1 /backup xfs
> rw,noatime,nodiratime,attr2,inode64,logbufs=8,logbsize=256k,noquota 0 0
> - Raid 10 with 1GB controller cache running in write back mode using 24
> spinners
> - no lvm
> - no io waits
> - xfs_info /serverbackup/
> meta-data=/dev/sda1              isize=256    agcount=21,
> agsize=268435455 blks
>          =                       sectsz=512   attr=2
> data     =                       bsize=4096   blocks=5369232896, imaxpct=5
>          =                       sunit=0      swidth=0 blks
> naming   =version 2              bsize=4096   ascii-ci=0
> log      =internal               bsize=4096   blocks=521728, version=2
>          =                       sectsz=512   sunit=0 blks, lazy-count=1
> realtime =none                   extsz=4096   blocks=0, rtextents=0
> 
> anything missing?
> 

What's the workload to the fs? Is it repeated rsync's from a constantly
changing dataset? Do the files change frequently or are they only ever
added/removed?

Also, what is the characterization of writes being "slow?" An rsync is
slower than normal? Sustained writes to a single file? How significant a
degradation?

Something like the following might be interesting as well:

for i in $(seq 0 20); do xfs_db -c "agi $i" -c "p freecount" <dev>; done

Brian

> > ... as well as what your typical workflow/dataset is for this fs. It
> > seems like you have relatively small files (15TB used across 350m files
> > is around 46k per file), yes?
> 
> Yes - most fo them are even smaller. And some files are > 5GB.
> 
> > If so, I wonder if something like the
> > following commit introduced in 3.12 would help:
> > 
> > 133eeb17 xfs: don't use speculative prealloc for small files
> 
> Looks interesting.
> 
> Stefan