Behaviour with reconstruct write on, still reading from destination drive.

[Mr.Cake]

Around 18 months ago i expanded my array by adding another 2 8tb disks, ever since then reconstruct write doesn't seem to work as it should.

With reconstruct write on unraid is still reading from the destination disk and also the parity disk. Slowing down operations to basically read/modify/write speeds. I've ignored it up until now.

Tried to google the answer myself but every post talks about slow write speeds not the fact that disk is still reading when it shouldn't be.

Pre array expansion with 'Turbo write' on i would see pure writing to destination and parity, now you see as below.

 

Anything i can do to fix this?

 

File copy from disk 1 > disk 3

Reconstruct write on

Reconstruct write off

unraid-diagnostics-20220824-1902.zip

Edited August 24, 2022 by Mr.Cake
grammar

[Kilrah]

That's because you're also reading from the array, when you do so it'll bounce back and forth between both modes. If your copy source is not on the array you'll see what you expect.

 

Full speed reconstruct write needs full read bandwidth from all drives, so if you're also reading from one it'll be impossible to achieve and you'll end up with pretty much the same situation than read-modify-write where a disk has to seek back and forth.

Edited August 24, 2022 by Kilrah

[Mr.Cake]

With reconstruct write / turbo write on you can copy and move files between disks in the array without any speed penalty. Which is how it was working before adding extra drives.

[JorgeB]

1 minute ago, Mr.Cake said:

With reconstruct write / turbo write on you can copy and move files between disks in the array without any speed penalty

No you cannot, it's as mentioned above.

[Mr.Cake]

Ok. Here is a copy from cache drive to drive 4 with turbo write enabled. Exhibits the same behaviour albeit with less reading.

[JorgeB]

Something else is still reading from that drive.

[Mr.Cake]

Yeah and that's my issue. What could it be? Or how can i find it.

[Kilrah]

You can try the "Open Files" plugin.

[Mr.Cake]

Since i haven't found a solution, I'm going to recreate the array to try and fix this.

 

Am I able to keep the cache drive as storage while removing all the spinners from the array? I'll be zeroing the drives if necessary, is there some way to have unraid forgot drive assignments so i can test if that fixes it first?

 

To be clear i've removed all plugins, docker is off, no vm's and it still happens. For whatever reason unraid feels the need to read from destination disk when it doesn't need to. The reading only occurs when you start a transfer. Would be great to know why this has happened though, won't be able to restart next time.

 

I think seafile might be breaking diagnostics , attach what it has grabbed before it fails.

unraid-diagnostics-20230115-0204.zip

[JorgeB]

20 hours ago, Mr.Cake said:

Am I able to keep the cache drive as storage while removing all the spinners from the array?

You can keep it intact but won't be able to used without any array devices assigned.

 

20 hours ago, Mr.Cake said:

is there some way to have unraid forgot drive assignments so i can test if that fixes it first?

Tools -> New config