Hello all,

  A few months ago I saw a statement that L2ARC writes are simplistic
in nature, and I got the (mis?)understanding that some sort of ring
buffer may be in use, like for ZIL. Is this true, and the only metric
of write-performance important for L2ARC SSD device is the sequential
write bandwidth (and IOPS)? In particular, there are some SD/MMC/CF
cards for professional photography and such, that can do pretty good
bursts at writes, and may be okay (better than HDD) at random reads
of the cached blocks.

  Are such cards fit for L2ARC uses?

  One idea I have is that a laptop which only has a single HDD slot,
often has SD/MMC cardreader slots. If populated with a card for L2ARC,
can it be expected to boost the laptop's ZFS performance?

  Also, what's the worst that is expected to happen if the card pops
out of its cardreader slot while it is used as L2ARC - should the
ZFS filesystem panic or fall back to HDD data seamlessly? Or does it,
as always, depend on firmware and drivers involved in the stack?


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