[SOLVED] Unraid Not Utilising Free RAM

[LumpyCustard]

Hi everyone,

 

First post here. Very new to Unraid, currently into my 2nd day of the trial and I've decided i'll be buying the pro tier and migrating my current Dell server.

 

I'm currently in the process of migrating approx 10TB of data from my old server to my Unraid server however I have noted that the sustained transfer speed seems to get progressively slower over the duration of the copy, starting at 150-200MB/s, and slowly going down to 50MB/s, then settling around 20-35MB/s. I have test copied from the source directly to my own computer and can confirm that it can deliver at least 100MB/s sustained.

 

See here:

 

Here is the copy from my server to Unraid:

 

The new server has 64GB of ECC RAM, 256GB cache drive, and all drives are connected to a PERC H310 running in IT / pass through mode.. During initial setup my parity drive was delivering 150-200MB/s write speed. Parity has since completed with no errors.

 

I have noted that over the last day my RAM is barely ever used. I'm permanently at 20-23% RAM usage (as a result of Windows 10 VM that i'm running), but otherwise the remainder of the RAM is not utilised in any way and sits dormant.

 

 

I'm wondering what I can do to improve performance, or at the very least tell Unraid to utilise RAM as cache more freely.

 

 

Edited March 8, 2020 by LumpyCustard

[trurl]

Do you have a cache drive? Are you writing to a cached share? 

[LumpyCustard]

Hello, thanks for the reply!

 

Yes, I mentioned above that I do have a cache drive. Have I set it up improperly from the screenshots below? I moved my VM to the cache drive as Windows 10 performance was abysmal on the array.

 

Note that the files I am copying at the moment are being sent to the "NAS" share. I selected the option "No" to cache on NAS because I did not want my NAS media files to be permanently stored on the cache due to the limited space on the SSD.

 

There is more free space in my RAM than there is in my cache, and i figured that Linux would freely use the available RAM but it simply isn't touching it.

 

Drives:

 

Shares:

 

Note that the transfer as of now has dropped down to 16MB/s

 

 

Edited March 4, 2020 by LumpyCustard

[JorgeB]

16MB/s is on the slow side even for normal write mode, but at least for the initial loading you want to use turbo write.

[LumpyCustard]

That has helped a lot, up to 75-80MB/s! Thank you!

 

Although is there anything I can do to coax Unraid into using more RAM? I don't like the fact that i have 40-50GB of RAM sitting around doing nothing.

 

Edited March 4, 2020 by LumpyCustard

[trurl]

12 hours ago, LumpyCustard said:

I selected the option "No" to cache on NAS because I did not want my NAS media files to be permanently stored on the cache due to the limited space on the SSD.

Cache-No means it won't use the cache at all. Cache-Yes means it will write to the faster cache then move them to the slower array at the scheduled time. Cache-Only will write them to cache and keep them there. Cache-Prefer is somewhat more complicated, but the effect is to try to keep (or even move) files to cache if there is room.

 

There is Help in the webUI. You can toggle Help for the whole webUI with Help(?) from the main menu, or you can toggle help for a specific setting by clicking on its label.

 

Here is a FAQ with more details on the various Use Cache Settings:

 

 

[trurl]

4 hours ago, LumpyCustard said:

Although is there anything I can do to coax Unraid into using more RAM? I don't like the fact that i have 40-50GB of RAM sitting around doing nothing.

What are you looking at to determine how much RAM is being used?

[LumpyCustard]

8 minutes ago, trurl said:

There is Help in the webUI. You can toggle Help for the whole webUI with Help(?) from the main menu, or you can toggle help for a specific setting by clicking on its label.

Thank you. I knew of the help section that expands when clicking on a setting but I guess i didn't read it properly. I have set the NAS share to "Cache: Yes" and confirmed mover is scheduled daily at 3am.

 

8 minutes ago, trurl said:

What are you looking at to determine how much RAM is being used?

On the dashboard page. Is the RAM info on this page obfuscating actual usage?

 

[JorgeB]

Any free RAM on Linux is used for cache, and that's not reflect on that graph.

[LumpyCustard]

Is this the case with htop as well? Apologies, new to Linux.

 

[trurl]

Dynamix System Stats plugin will also let you see the cache RAM if you really want to see it, but as mentioned

4 minutes ago, johnnie.black said:

Any free RAM on Linux is used for cache

 

[LumpyCustard]

Thanks for the help everyone. I'm marking this topic as solved as my RAM question was answered (my lack of understanding of Linux RAM management) and enabling turbo write substantially improved write performance.

[mgutt]

@LumpyCustard

You could install the Tips and Tweaks Plugin and raise the vm.dirty_ratio to 50% to use 50% of your free RAM as your writing cache (linux default is 20%):

https://forums.unraid.net/topic/47457-tips-and-tweaks-page/?tab=comments#comment-468078

 

By default Linux will use 100% of your free RAM as your read cache.

 

More infos in #7 of my guide:

https://forums.unraid.net/topic/97165-smb-performance-tuning/

 

Edited November 15, 2020 by mgutt