copying milllions of small files and millions of dirs

[Charles Swiger]

On Aug 15, 2013, at 11:37 AM, aurfalien <aurfalien at gmail.com> wrote:
> On Aug 15, 2013, at 11:26 AM, Charles Swiger wrote:
>> On Aug 15, 2013, at 11:13 AM, aurfalien <aurfalien at gmail.com> wrote:
>>> Is there a faster way to copy files over NFS?
>> 
>> Probably.
> 
> Ok, thanks for the specifics.

You're most welcome.

>>> Currently breaking up a simple rsync over 7 or so scripts which copies 22 dirs having ~500,000 dirs or files each.
>> 
>> There's a maximum useful concurrency which depends on how many disk spindles and what flavor of RAID is in use; exceeding it will result in thrashing the disks and heavily reducing throughput due to competing I/O requests.  Try measuring aggregate performance when running fewer rsyncs at once and see whether it improves.
> 
> Its 35 disks broken into 7 striped RaidZ groups with an SLC based ZIL and no atime, the server it self has 128GB ECC RAM.  I didn't have time to tune or really learn ZFS but at this point its only backing up the data for emergency purposes.

OK.  If you've got 7 independent groups and can use separate network pipes for each parallel copy, then using 7 simultaneous scripts is likely reasonable.

>> Of course, putting half a million files into a single directory level is also a bad idea, even with dirhash support.  You'd do better to break them up into subdirs containing fewer than ~10K files apiece.
> 
> I can't, thats our job structure obviously developed by scrip kiddies and not systems ppl, but I digress.

Identifying something which is "broken as designed" is still helpful, since it indicates what needs to change.

>>> Obviously reading all the meta data is a PITA.
>> 
>> Yes.
>> 
>>> Doin 10Gb/jumbos but in this case it don't make much of a hoot of a diff.
>> 
>> Yeah, probably not-- you're almost certainly I/O bound, not network bound.
> 
> Actually it was network bound via 1 rsync process which is why I broke up 154 dirs into 7 batches of 22 each.

Oh.  Um, unless you can make more network bandwidth available, you've saturated the bottleneck.
Doing a single copy task is likely to complete faster than splitting up the job into subtasks in such a case.

Regards,
-- 
-Chuck