Hi guys, I recently ran into a problem. I run win 10vm on unraid and use ssd cache pool of two cheap wd green 120gb for vdisk, docker and appdata.

recently noticed a strange thing:

when I copy files from cache pool to vdisk the speed is slow (45-50MB/s)

when I copy files from vdisk to cache pool - same speed!

when I copy files from vdisk to array and vice versa, speed is 170MB/s

why array is faster than cache??? are these WD green so slow??

tried changing fx440, q35

vdisk share - "cache only"

appdata share - "cache only"

system share - "cache only"

what I missed?

TRIM every 8 hours, 50GB free space

 

UPD: using MC I tried to copy big file direct from array to cache (/mnt/user/backup > /mnt/cache) 55MB/s !

 

very much like low ssd disks performance or btrfs raid1 performance!

what tests do you recommend to do? 

should i try convert pool to single device for additional speed tests?

Edited March 3, 20188 yr by vanes

Copying between a vdisk and the cache will be slower when the vdisk is also on the cache as you will get a certain amount of disk thrashing as you try to read and write to different parts of the same disk(s)

what speed other users get when writing from vdisk to cache?

Edited March 3, 20188 yr by vanes

I think most people would be using SSD in such a Use case so their speeds would not be adversely affected by head movements so their speeds would not be comparable.

So?you want to say 50MB/s write from array to cache pool is normal?

Later I will do tests with out: 

dockers (copy to vdisk from cache)

vm`s (just copy from array to cache) 

Edited March 3, 20188 yr by vanes

I read , watched some reviews and knew that 50-60MB/s is normal write speed for this WD Green ssd! 

 

do not repeat my mistakes do not buy them!!!!

this is write from vdisk to cache

this is write from vdisk to array with parity!!!! wd blue 1TB 7200rpm

Edited March 3, 20188 yr by vanes

16 minutes ago, vanes said:

I read , watched some reviews and knew that 50-60MB/s is normal write speed for this WD Green ssd!

That's normal for any 120GB TLC SSD, they max out at about 70/80MB/s sustained writes, 120GB 850 EVO can do 150MB/s, 250GB can do 300MB/s sustained.

Replaced slow wd green with Samsund 850 120Gb x2 Raid1. 

Some users report low write performance on this disks, freezes... etc 

In my cases, I do not see any problems. Only good performance

 

i am runnin win10 vm on 50Gb vdisk, and this is coping from array to vdisk which is on cache pool raid1. Wd Green`s speed was only 50 mb/sec.