Slow write performance

[ulf]

Have build a FreeNAS server running 8.3.1-p2
Based on an AMD E-450 with 16 GB RAM.
4 x 3 TB disks WD RED running ZFS
The volume is now 67% used (3.5TiB) with 1.7TiB Free.

Connected to a Core-i7/940 machine over a D-Link DIR_685 storage router.

I used it mainly to store MP4 copies of movies recorded on DVD+R.
Typically, it used to take about 15 minutes to convert a DVD directly to the NAS,
and now it suddenly takes almost an hour.

Tried to figure out why, so I first copied the DVD to a hard drive.
This did not change conversion time, but when I changed output
directory from the NAS to a disk, it was back at normal speed.

If I copy a large file to the NAS (1 GB), then it copies at 4-5 MB / second,
which seems quite slow.

I read somewhere, that the size of the DRAM is critical when running ZFS.
Have I reached a limit on DRAM and need more than 16 GB
(Thats the MAX supported by the motherboard)?

Any other reason for the real slow write speed?

 

[cyberjock]

That sounds like you may have a failing disk.

Post the output of the command smartctl -a -q noserial /dev/(yourdiskhere)

Remember to post it for all of your disks. :)

 

[ulf]

OK, here are the selftest in an attached file.
Tried again, and I now get 11-12 MB/s but conversion time still ~45 minutes.
I rebooted right before I tested a file copy, and maybe the system was busy scanning for files
during the first test.
The reason for reboot was the slow write performance though.

When I look at reports, I noticed that CPU was at 100% running mostly in system.
Now it has dropped to normal ratings, and write speed is OK again.
No clue why.

Physical memory seems to have around 0.5-1GB free

 

[ulf]

Looked at the history of the "CPU Usage" log.
Apparently, the system is doing something on Sundays once a month,
because the CPU usage goes up to 100% and stays there between 0:00 and 9:00.

 

[gpsguy]

It might be scrubbing your pool. Do a:

zpool status -v

to see when it was last run

Sent from my phone

 

[cyberjock]

Your hard drive looks good. I bet it was a scrub come to think of it.

 

[pbucher]

Has you add more files the scrub will take longer, hence why you are just now noticing it.