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Hi all. Sorry if I am asking a FAQ, but I haven't found a really
authorizative answer to this. Most references are old, incomplete or
of "I have heard of" kind.

I am running Solaris 10 Update 9, and my pool is v22.

I recently got two 40GB SSD I plan to add to my pool. My idea is this:

1. Format each SSD as 39GB+1GB.
2. Use the TWO 39GB's as L2ARC, with no redundancy.
3. Use the TWO 1GB's as mirrored ZIL.

1GB of ZIL seems more than enough for my needs. I have synchronous
writes, but they are, 99.9% of the time, <1MB/s, with occasional bursts.

My main concern here is about pool stability if there have any kind of
problem with the SSD's. Especifically:

1. Is the L2ARC data stored in the SSD checksummed?. If so, can I
expect that ZFS goes directly to the disk if the checksum is wrong?.

2. Can I import a POOL if one/both L2ARC's are not available?.

3. What happend if a L2ARC device, suddenly, "dissappears"?.

4. Any idea if L2ARC content will be persistent across system
rebooting "eventually"?

5. Can I import a POOL if one/both ZIL devices are not available?. My
pool is v22. I know that I can remove ZIL devices since v19, but I
don't know if I can remove them AFTER they are physically unavailable,
of before importing the pool (after a reboot).

6. Can I remove a ZIL device after ZFS consider it "faulty"?.

7. What if a ZIL device "dissapears", suddenly?. I know that I could
lose "committed" transactions in-fight, but will the machine crash?.
Will it fallback to ZIL on harddisk?.

8. Since my ZIL will be mirrored, I assume that the OS will actually
will look for transactions to be replayed in both devices (AFAIK, the
ZIL chain is considered done when the checksum of the last block is
not valid, and I wonder how this interacts with ZIL device mirroring).

9. If a ZIL device mirrored goes offline/online, will it resilver from
the other side, or it will simply get new transactions, since old
transactions are irrelevant after ¿30? seconds?.

10. What happens if my 1GB of ZIL is too optimistic?. Will ZFS use the
disks or it will stop writers until flushing ZIL to the HDs?.

Anything else I should consider?.

As you can see, my concerns concentrate in what happens if the SSDs go
bad or "somebody" unplugs them "live".

I have backup of (most) of my data, but rebuilding a 12TB pool from
backups, in a production machine, in a remote hosting, would be
something I rather avoid :-p.

I know that hybrid HD+SSD pools were a bit flacky in the past (you
lost the ZIL device, you kiss goodbye to your ZPOOL, in the pre-v19
days), and I want to know what terrain I am getting into.

PS: I plan to upgrade to S10 U10 when available, and I will upgrade
the ZPOOL version after a while.

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