On Tue, 8 Jun 2021, Reginald Beardsley via illumos-discuss wrote:
Using the NVMe as an L2ARC seems likely to wear it out faster than
forcing reads to come from the SSD and writes to go to disk. As I
understand it, nothing can appear in the L2ARC except by being in
the ARC first.
According to Lucas and Jude, at the time of writing (ca 2016), the
L2ARC index does not get saved across a reboot. If that has changed
so that all the underlying filesystem is fully cached in the SSD if
the L2ARC is larger than the filesystem, that seems the best route.
Otherwise reboots may cause significant wear.
As you say "nothing can appear in the L2ARC except by being in the ARC
first".
It can take considerable time for data to be initially read and expire
from the ARC and thus be moved to L2ARC. Unless the device you bought
is particularly fragile, it seems difficult to believe that it is
going to wear out due to writes. I am not sure if Illumos supports
the persistent L2ARC feature, but if it does, then that would be
helpful for start-up performance.
If an SSD and a disk form a mirror, which will satisfy the reads and
at what speed? Can one half of a mirror be a RAIDZ2 filesystem?
You can use a SSD and a disk to create a mirror. The reads may occur
more often on the SSD due to better latency. The writes will be as
slow as the disk. To me this seems like a bad trade-off.
It is possible to stack zfs storage pools but that is not recommended.
Bob
--
Bob Friesenhahn
[email protected], http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
Public Key, http://www.simplesystems.org/users/bfriesen/public-key.txt
------------------------------------------
illumos: illumos-discuss
Permalink:
https://illumos.topicbox.com/groups/discuss/T9dbd246b28a51627-Me814217b176a8d3371efc44c
Delivery options: https://illumos.topicbox.com/groups/discuss/subscription
