Parity check three times slower than sync or rebuild. Is it normal?

[JorgeB]

You appear to have the same issue I have, at first I though it affected both parity check and disk rebuilds and not parity sync, but after some new quick tests it only slows down during parity check.

 

Also just found out during this tests that at least on my test server there’s a big difference if I connect the disks to the SAS2LP in order, parity to port 0, disk 1 to port 1, etc.

You can try it on your server if they are not in order, although still far from what it should be on this server (around 200Mb/s), there's a huge difference, I’ll have to try it on my other servers.

 

Disk rebuild

 

Parity Check (disks connected in random order)

 

Parity Check (disks in order)

 

[KentBrockman]

johnnie

 

Thanks for the suggestion.  I re-arranged my drives like this:

 

Parity - MB Slot 1

Disk 1 - MB Slot 2

Disk 2 - MB Slot 3

Disk 3 - MB Slot 4

Disk 4 - SAS2LP Port 1

Disk 5 - SAS2LP Port 2

Disk 6 - SAS2LP Port 3

Disk 7 - SAS2LP Port 4

Disk 8 - SAS2LP Port 5

cache - SAS2LP Port 6

 

Parity check speed did improve a little bit.  I averaged 52 Mb/s last run.

It started slow (25 30 MB/s) but got faster as I passed about 50%.

 

 

[JorgeB]

I don’t know why and I’m still testing but it does make a difference, in one of my servers only works if the parity and first 7 disks are connect to the sas2lp and the rest to the onboard ports, all in order, parity check went from 40Mb/s to around 80Mb/s.

 

There’s still an issue with the SAS2LP and this is not a fix, just minimizes the issue, I still hope it will be fixed someday.

 

Kent, you should also run tunables tester, especially if you’re using default values, you can gain another 10 to 30Mb/s.

 

[TODDLT]

Well, not knowing about this issue, I just bought a SAS2LP on sale this past week and ran right into the problem.  Since people are working on it, I just thought this snapshot was interesting.  here are the charts showing my CPU utilization and Drive speed during a parity check.  My configuration in my signature is current.

 

I'm not sure that this is useful or not but it seems to be ramping up/down continuously. 

 

[TSM]

Since people are working on it

I don't think this issue is on Limetech's radar.