On 2018-06-19 06:55, Bowie Bailey wrote:
On 6/19/2018 1:35 AM, Michael Schumacher wrote:
Hi there

Friday, June 15, 2018, 3:06:30 PM, you wrote:

BB> It finally finished after 24 hours.  That gives about 13G/hour or about
BB> 3.8M/s.

BB> The CPUs were not busy.  That's what I was confused about.  I would have BB> expected to see a bottleneck at some point, but nothing seemed to be BB> busy.  The CPUs were all at or below 20% and iowait was close to 0 most BB> of the time.  I'm not sure how I would determine if the loopback was
BB> saturated.

what file system are you using? I am operating a mailserver on a
dedicated machine. There are some millions of small files on that
machine, so the situation is comparable to yours. When I set up that
machine some years ago, I compared various file systems. Surprisingly,
ext4 came out as winner to handle these small files. I am just using
ext4 on top of the hardware, no lvm on that machine. And of course
having a lot of RAM may also speed up your machine, because the server
can read ahead data. I think it may be a matter of tuning that server
to get better performance.
give some hints on read ahead tuning.

The backup server is xfs.  I haven't looked into performance tuning,
since most of my servers are not doing enough IO to need it.

It's probably worth mentioning that I experienced a slowness problem on xfs, specifically.

Repeated (forced, offline) fscks sometimes turned up subtle filesystem issues, and sometimes reported everything was ok. The symptoms were slowness, and occasional hangs in rsync. My test results:

* Moving all files to a new jfs filesystem. Performance improved. No hangs. * Moving all files to a new xfs filesystem. Performance improved. No hangs. * Moving all files to a new ext4 filesystem. Performance improved. No hangs. * Moving all files back to the same physical drives, btrfs. Performance improved. No hangs.

My conclusion at the time was that some kind of corruption or decay had crept into the xfs filesystem over time. The physical drives were perfectly fine. I did not diagnose further, but I did abandon xfs and have not had further issues.
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