Is this a slow scrub speed?

[Lorsung23647]

I recently migrated to FreeNAS from another product, and imported my pools over the weekend. After the import I decided to start a scrub just to verify my data. I've never had what I considered a slow scrub until I started reading here and seeing people with 3 disk Z1's getting 200-400 MB/s scrubs, or 12 disk Z3's with 1 GB/s+ scrubs.

I have a 6 disk Z2 pool using 4TB Seagate NAS drives that starts a scrub at ~90 MB/s and ends around 250 MB/s. Processor usage during the scrub never goes above 40% and averages 12%. Disk usage as reported by gstat seems to over around 40% for all drives as well, with randomly timed spikes on 2 random disks up to 60-80% that never last past the next refresh.

My system is running FreeNAS 9.2.1.2 64 Bit, using a XEON E3-1230 v2 processor and 32GB of ECC RAM. I have a LSI 9201-16i and a LSI 9211-8i HBA in the system that all of my disks are hooked up to.

I have a few other pools in the system as well, but nothing that should be maxing the bandwidth of my HBAs out, all of those report the same behavior during scrubs as well.

 

[cyberjock]

There is no 'fast" or "slow" scrub. It's based on many factors such as how full the pool is, how fragmented your files are, etc. So unless you can tell us it used to do 800MB/sec and now its suddenly 250MB/sec, there's no way to know if "there's a problem" or not. My pool can do over 1GB/sec, but its not consistent throughout the scrub. Parts are limited to 50MB/sec or less, others over 1GB/sec.

 

[Lorsung23647]

Most of my data is media and vm stores, and the pool is only about 40% full. But mine doesn't seem to speed up or slow down at any point, it's just a linear scale as the scrub goes along. I've never seen parts where the speed drops or rises suddenly, at least monitoring with zpool status -v 10. If that doesn't seem odd, great! I just wish I could see a magical uber fast scrub.

 

[cyberjock]

VM stores are almost always HEAVILY fragmented. So yeah, I'd expect the slower end of the spectrum unfortunately. :(

 

[Lorsung23647]

Ah, well at least it's expected. Thanks for the answer.