l2arc rsync metadata

[retroman]

hi,

I have a 48 gb freenas with 10x8tb raidz2
It serves as a daily backup via rsync wan for 20 synology. maybe 2 millions files. Not a lot of changes.
If I start >4 simultaneous rsync, drives are suffering
Do you think an ssd configured as a l2arc metadata would improve rsync ?
Which size would you recommend ?

 

[retroman]

Ok I added an ssd samsung 120gb 840. Everything is fine. Some rsync seems to be twice as fast.

Now I found some memory and upgraded to 72gb.

I may replace my l2arc for 1tb.
How can I know l2arc is too big ? Is there any tutorial for easy reading arc/l2arc reporting ?