SOLVED Questions about cache and ZFS Arc Size / ZFS Arc Hit Ratio

[lord.anonymous]

Hello !
First I'm french, so I hope you'd understand me, I'll do my better !

I use Freenas since a long time (2012), but I'm not a specialist.

My system :

• Supermicro Motherboard (I don't know the model)
• Intel(R) Xeon(R) CPU X3430 @ 2.40GHz (4 cores)
• 32 GB Ram ECC (Maxi for this motherboard)
• 4*4To (Raid Z1 / no ZFS dedup / no compression) --> MULTIMEDIA POOL (movies, musics, etc)
• 4*3To (Raid Z2 / ZFS dedup / lz4) --> IMPORTANT POOL (personnal docs, virtual disks for VMs, stuff for my music bands like videos, etc)

My issue :

• Copy from MULTIMEDIA POOL to Win10 : no problem with large files (more than 2GB)
• Copy from Win10 to MULTIMEDIA POOL : no problem with large files
• Copy from IMPORTANT POOL to Win10 : no problem with large files
• Copy from Win10 to IMPORTANT POOL : problem with large files... copy often stops ... need to restart the copy ...

I suspect that ZFS Deduplication and LZ4 compression was a bad idea. But it's made, now, I won't rebuilt this pool.
It's like this for years, it's just a little annoying, I can continue like that... but I wonder about SSD cache...
I join screen captures for understand.

My question :

• Will a 128 GB SSD cache for this IMPORTANT POOL change something ?

Thanks everyone !

Pierre

 

[Patrick M. Hausen]

Compression is a good idea while deduplication in general isn't. Can't you just switch it off again for the pool/datasets in question?
I don't use that feature but I had the impression that it is a ZFS property that can be switched on and off at will. Only applies to newly written data, of course.

 

[lord.anonymous]

It was so simple :D
Why didn't I think about it before ?

Works great now, first time I can copy a 10GB file without any failure !
Thanks a lot !!! :)

 

[sretalla]

Will a 128 GB SSD cache for this IMPORTANT POOL change something ?

With that little RAM, it will certainly not help. L2ARC uses RAM to store metadata, which will decrease the amount of RAM remaining for ARC.
The usual advice in this forum is to look at L2ARC when you have already installed 64GB of RAM or more and still see the possibility of more files changing than the available RAM.

Perhaps you need to consider turning off deduplication as suggested (which also requires a very large amount of RAM... more than 1GB per TB).

 

[lord.anonymous]

With that little RAM, it will certainly not help. L2ARC uses RAM to store metadata, which will decrease the amount of RAM remaining for ARC.
The usual advice in this forum is to look at L2ARC when you have already installed 64GB of RAM or more and still see the possibility of more files changing than the available RAM.

Perhaps you need to consider turning off deduplication as suggested (which also requires a very large amount of RAM... more than 1GB per TB).

Yes, I did it, and it resolves my issue.
Thank you for your answer !