RAM amount recommendations for ZFS pools with ZIL and L2ARC on SSD

[Miroslav Lachman]

Zeus Panchenko wrote:
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> hi all,
>
> while discovering the subj, I found recommendations at:
> http://doc.freenas.org/index.php/Hardware_Recommendations#RAM
>
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> ... a general rule of thumb is 1 GB of RAM for every 1TB of storage ...
> If you plan to use ZFS deduplication, a general rule of thumb is 5 GB
> RAM per TB of storage to be deduplicated.
> - ---------------------------------------------------------------------
>
>
> so, are these recommendations correct for ZFS pools with ZIL and L2ARC
> on SSD configurations?
>
> are there corellations between "RAM amount" and "with/without ZIL, L2ARC
> on separate devices pool configuration" ?

The bigger L2ARC you have, the more RAM you need to store metadata about 
"what is in L2ARC". So if you have some system without L2ARC and you 
will add SSD as L2ARC, then you will need more RAM than before.
It depends on records size and number of records stored in L2ARC.

You can take a look at this thread

http://www.mail-archive.com/zfs-discuss@opensolaris.org/msg34674.html
http://www.mail-archive.com/zfs-discuss@opensolaris.org/msg34677.html

Miroslav Lachman