allow for persistent l2arc

[cwedgwood]

https://groups.google.com/a/zfsonlinux.org/forum/?fromgroups=#!topic/zfs-discuss/eSYYLdx73r4

References request and a suggestion on how it might be done.

[mlidbom]

Seems there's an implementation of this in illumos going through final testing now:
Feature Request
Design Document
Patches
I would love to see it implemented for linux.

[behlendorf]

Once it's merged in to Illumos in it's final form and soaks for a while I'm sure we'll pick this up.

[yshui]

Are there anyone interested in doing this? Otherwise I'll try porting and keeping track of this patch set.

[behlendorf]

@yshui Nobody on the Linux side I know if working on this right now. If you can port the upstream patches and keep them up current that would be great. I'm sure @skiselkov would appreciate any additional testing and feedback you can provide.

[grahamperrin]

From irc://chat.freenode.net/#illumos today:

nexenta might have some kind of implementation for it, i think.

[kernelOfTruth]

@grahamperrin thanks for the pointer !

Nexenta/illumos-nexenta@f0a9ee9 NEX-3514 Implement persistent L2ARC

Nexenta/illumos-nexenta@8872632 NEX-3514 Implement persistent L2ARC - fix build breakage in libzpool.

Nexenta/illumos-nexenta@9498bb1 NEX-3514 Implement persistent L2ARC - fix build breakage in libzpool (v2).

https://github.com/Nexenta/illumos-nexenta/commits/master?page=4

[kerberizer]

illumos 3525 is now in code review.