Pri - has 4 x 16TB Ironwolf-Pro (CMR)
Sec - has 6 x 4TB WD-RED (CMR)
Nas’es are just on in the weekend , when doing backup & ZFS replication from Pri. to Sec.
This weekend i was doing my weekly backups, and it was time for a monthly scrub, after the backup & replication was done.
My “Rust-Pools” have - Approx 5.8 TB data , and Sec ZFS contains replicated images of Pri datasets. AKA same data.
I was starting the scrub’s at the same time , but the Sec. finished almost an hour before the Pri.
That surprised me a bit, because when doing some RW tests, the 16TB IW-Pro’s was quite a bit faster than the “Older” WD-RED’s.
Q1:
Is that because of the 6-disk layout vs 4-disk ?
I also ran an “Extended smart test” (EST) , and it took almost 24h for the 16TB IW-Pro’s.
Q2:
Since my NAS’es “just” logs around 80h running time per month.
Could i delay the “EST” to ie. every 3 month (240h) ?
That would be the equivalent to 10 days on a 24/7 system.
I always thought scrub based on how much data on the drive + layout … not actual drive size?
second - your secondary - I’m guess won’t have has much load as the primary - since it just to backup - so it had more time to get involved with scrub.
Both NAS’es was 100% Idle when doing the Scrub.
All backup & replication was done.
No Smart test was started yet.
It could be Sata or CPU HW , but none was loaded more than around 30% peak cpu, at times.
Or Ram ?? - Even though i would expect the xfer rate of spinning disks to be quite slow compared to Ram speed.
Pri (Home) has 32GB
Sec (backup) has 64GB
See “Bottom tags” for HW desc.
Maybe a RZ2-6 has higher data throughput than a RZ2-4 layout.
Most likely. These old WD Red may be slower than the IronWolves, but reading from six of them instead of six must deliver more throughput.
Having more RAM never hurts with ZFS…
Not directly related to your question as this was an extreme case, NOT having enough RAM (namely dedup with “only” 64 GB) can slow scrub to a painful crawl.
I suspect that could be part of it but you are not comparing similar machines either. The only common items are the case, boot drive, that is it.
Your backup NAS has faster RAM, faster CPU. You are also using six SATA cables which can transfer more data than the four in the other machine.
A test: Move the 4 drives to the 6 drive machine and a copy of the setup, then scrub it. Compare the time between the machines and you will have your answer to “It is the machine or pool layout?”
