ZFS: Memory needed for managing L2ARC

[Miroslav Lachman]

Dmitry Morozovsky wrote:
> Dear colleagues,
>
> are there any "real" estimations on how much memory is needed for having
> efficient, say, 1T of L2ARC?  stable/amd64, of course.
>
> I have backup storage server, where pool size is targeted to a few hundreds of
> terabytes (currently ~35T), and hot set is usually less than 512G-1T.
>
> quick googling leads to some Solaris/Illumos documents, but even them are not
> bright enough in answer that.

I have some old informations in a bookmarks:

Re: [zfs-discuss] ZFS ZIL + L2ARC SSD Setup
http://www.mail-archive.com/zfs-discuss@opensolaris.org/msg34674.html

Approximately 200 bytes per record. I use the following example:
         Suppose we use a Seagate LP 2 TByte disk for the L2ARC
                 + Disk has 3,907,029,168 512 byte sectors, guaranteed
                 + Workload uses 8 kByte fixed record size
         RAM needed for arc_buf_hdr entries
                 + Need = ~(3,907,029,168 - 9,232) * 200 / 16 = ~48 GBytes


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

I hope this helps

Miroslav Lachman