Ext3 users - Jun 2011 - How long should resize2fs take?

Hullo!

First mail, sorry if this is the wrong place for this kind of
question. I realise this is a "piece of string" type question.

tl;dr version: I have a resizefs shrinking an ext4 filesystem from
~4TB to ~3TB and it's been running for ~2 days. Is this normal?

Strace shows lots of:-

lseek(3, 42978250752, SEEK_SET)         = 42978250752
read(3,
"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"...,
4096) = 4096
lseek(3, 4675072176128, SEEK_SET)       = 4675072176128
read(3,
"\355A\350\3\0\20\0\0009\271\371M\206\177\0N~\206\33M\0\0\0\0\350\3\2\0\10\0\0\0"...,
4096) = 4096
lseek(3, 42978254848, SEEK_SET)         = 42978254848
read(3,
"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"...,
4096) = 4096
lseek(3, 42978238464, SEEK_SET)         = 42978238464
write(3,
"\355A\350\3\0\20\0\0009\271\371M\364Y\4N\200\206\33M\0\0\0\0\350\3\2\0\10\0\0\0"...,
4096) = 4096
lseek(3, 4675072180224, SEEK_SET)       = 4675072180224
read(3,
"\355A\350\3\0\20\0\0009\271\371M\206\177\0N~\206\33M\0\0\0\0\350\3\3\0\10\0\0\0"...,
4096) = 4096
lseek(3, 4675072163840, SEEK_SET)       = 4675072163840
write(3,
"\355A\350\3\0\20\0\0009\271\371M\206\177\0N\200\206\33M\0\0\0\0\350\3\2\0\10\0\0\0"...,
4096) = 4096

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
32719 root      20   0  785m 768m  792 R   98 20.0   2443:18 resize2fs

$ sudo resize2fs /dev/mapper/data-data 3000G
resize2fs 1.41.11 (14-Mar-2010)
Resizing the filesystem on /dev/mapper/data-data to 786432000 (4k) blocks.

Time passes. :D

It's an LVM comprising 4x2TB disks in RAID10 and 4x500GB in RAID10.

$ cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid10] [raid6]
[raid5] [raid4]
md1 : active raid10 sdi1[0] sdg1[1] sdf1[3] sdh1[2]
      976767872 blocks 64K chunks 2 near-copies [4/4] [UUUU]

md0 : active raid10 sda1[2] sdc1[3] sdb1[1] sdd1[0]
      3907023872 blocks 64K chunks 2 near-copies [4/4] [UUUU]

Disks are 7200RPM SATA disks.

It's ~2TB full of data which is mostly rsnapshots of lots of remote
hosts, so lots of little files.

Cheers,
Al.

On Fri, Jun 24, 2011 at 10:48:51AM +0100, Alan Pope
wrote:
> Hullo!
> 
> First mail, sorry if this is the wrong place for this kind of
> question. I realise this is a "piece of string" type question.
> 
> tl;dr version: I have a resizefs shrinking an ext4 filesystem from
> ~4TB to ~3TB and it's been running for ~2 days. Is this normal?
Shrinking a file system can take a long time; it depends on how many
files are using space in the part of the file system that needs to be
evacuated for the shrink to take place.
> It's ~2TB full of data which is mostly rsnapshots of lots of remote
> hosts, so lots of little files.
Yes, that will take longer.  Resize2fs is engineered for safety, which
means it copies a lot of blocks, and then it updates the inodes, and
then copies more blocks, and then updates the inode involved, etc.  So
it's a fairly seeky operation that can take a while.

Most of the time people are growing their file systems, not shrinking
them, so we haven't done a huge amount of optimization for speed in
the shrink case.

Regards,

					- Ted