Write performance dips

[TheBekker]

I just noticed today when i had to copy a large file to my Unraid array.
I started out good with about 80-100 mb/s, but after a while it drops down to 5-15mb/s.

Its a 4 disk array with 1 being parity + 1 SSD Cache (though cache is not enabled on the share im copying to)..
Using all WD Blacks 7200rpm drives.

Any ideas what could be causing this?

Edited July 26, 2017 by TheBekker

[tdallen]

The 80-100 MB/s is reflective of in-memory caching on your server, and it slows down when it exhausts the RAM available for cache.

 

All WD Black 7200rpm drives are not created equal - I have some old/small ones that are very slow.  How recent are yours?  Also, are you copying one large file, or lots of small ones?

[TheBekker]

My server has 48Gigs of ram, and doesn't seem to fill up.

They are all from Feb. this year.
I'm copying about 40 files, ranging from 1.5gb to 4gb in size.

I just tried to enable my cache drive on the share i'm copying to, and that seems to fix the issue.
Just seems strange that i would need SSD cache to achieve a stable 80-100 mb's

[JorgeB]

Only 20% of the RAM is used for caching by default, other option is to enable turbo write, you should be able to achieve line speed with gigabit.

 

 

[TheBekker]

10 minutes ago, johnnie.black said:

Only 20% of the RAM is used for caching by default, other option is to enable turbo write, you should be able to achieve line speed with gigabit.

 

 

Quite interesting, i'll look in to that and do some tests  thanks