Hi guys,

I have a very stange Problem. Somtimes one of my disks is very slow. Every time this happens its only one of the two drives. I've changed the SATA cables and the mainboard and RAM ( for an other reason ) and still it happens. Any clue?

 

unraid-server-diagnostics-20240422-0729.zip

That looks more like a disk issue.

And which disk? It happens on on both ones. Some times the one sometimes the other. However, it’s always only one of the two.

I thought it was only one of them, in that case much less likely that a disk is the problem, but don't really have other ideas, there's nothing out of the ordinary logged in the syslog, very strange issue.

Hmmm strange. I was thinking that it’s an hardware issue. However, after changing the whole system except the drives and the PSU, I still have the problem. I think with switching the SATA  cable, I can move  the problem from one to the other device.

Could it be a driver issue?

54 minutes ago, muko said:

Could it be a driver issue?

Don't really think so, controller is using the stock AHCI driver, I guess it could be a controller/board problem.

22 minutes ago, JorgeB said:

Don't really think so, controller is using the stock AHCI driver, I guess it could be a controller/board problem.

But how likely is it that the same problem is on two different bords. Fun fact: I didnt touch anything since I run the speedtest last time. System was powered all the time. Now I just run the test again and boths HDD are at full speed. Magic

11 hours ago, muko said:

Somtimes one of my disks is very slow.

Are you positive nothing else was trying to access the drive during the test?

7 minutes ago, JonathanM said:

Are you positive nothing else was trying to access the drive during the test?

Yeah, more or less. As one drive is the parity and other one is  drive1.

I m new to unraid so I don’t know wether there are scenarios when parity only is accessed by anything and not the data?

Parity will not be accessed for any array reads, it will be access during a parity check or any array writes.

44 minutes ago, JonathanM said:

Are you positive nothing else was trying to access the drive during the test?

 

20 minutes ago, JorgeB said:

Parity will not be accessed for any array reads, it will be access during a parity check or any array writes.

In that case I'm very positive

Hi again,

sorry for the double post. I did some further testing today. What I did:

1) I moved all my drives to yet an other PC. Exept of the two HDD the NVME cache and the USB drive every pice of hardware was different.

Result was that the issue didnt. change. Still one drive was very slow.

2) I then createt usb drive with a fresh unraid test version install. I used a NVME drive that I had laying around as my array and put everything back in my "old" PC. Just installed the unassigned divece plugin and diskspeed.  
The result was both drives at full speed.

3) I replaced the fresh USB drive with my "production" one reinserted my cache drive and voila the error is back.

 

Interesting to add here that again the error moved from one drive to the other comparing the situation before step 1 and after. For me it seems that it realy comes down to the unraid installation ?!?

 

An other thing I noticed during doin all of that. Starting the array takes like ages. So I would also exclude a lot of processes that are started after the array is running.

 

Edit: Ok I think I now identified the error. However, I still don't fully understand it. Maybe you can help me out.. I noticed that ZFS scrup was running. When I stoped that, we're back at full speed. I still don't understand why it's sometimes the one and sometimes the other drive? Can anyone explain that for me?

 

Edit 2: I think I have the full picture now. I just made an other little experiment. I started scrub and did the speed test. I figured that my main drive was slow. Parity at full speed. I did that test several times. Next I shuted down the PC and switched the sata cable between the two drives. After reboot I started scrub again and I did an other speed test. Now my party was slow. 

Here comes the thing: Disk Speed Scans the SATA controllers once. It won't recocnize if you switch SATA cable. So after switching my main drive was shown as parity and vice versa. After hitting that rescan button the main drive speed test is the slower one again. My goodness, that cost me some of my life. I was about to buy some new drives ;(

Edited April 23, 20242 yr by muko