On Jun 11, 2008, at 1:16 AM, Al Hopper wrote:
But... if you look
broadly at the current SSD product offerings, you see: a) lower than
expected performance - particularly in regard to write IOPS (I/O Ops
per Second)
True. Flash is quite asymmetric in its performance characteristics.
That said, the L2ARC has been specially designed to play well with the
natural strengths and weaknesses of flash.
and b) warranty periods that are typically 1 year - with
the (currently rare) exception of products that are offered with a 5
year warranty.
You'll see a new class of SSDs -- eSSDs -- designed for the enterprise
with longer warranties and more write/erase cycles. Further, ZFS will
do its part by not killing the write/erase cycles of the L2ARC by
constantly streaming as fast as possible. You should see lifetimes in
the 3-5 year range on typical flash.
Obviously, for SSD products to live up to the current marketing hype,
they need to deliver superior performance and *reliability*.
Everyone I know *wants* one or more SSD devices - but they also have
the expectation that those devices will come with a warranty at least
equivalent to current hard disk drives (3 or 5 years).
I don't disagree entirely, but as a cache device flash actually can be
fairly unreliable and we'll pick it up in ZFS.
So ... I'm interested in learning from anyone on this list, and, in
particular, from Team ZFS, what the reality is regarding SSD
reliability. Obviously Sun employees are not going to compromise
their employment and divulge upcoming product specific data - but
there must be *some* data (white papers etc) in the public domain that
would provide some relevant technical data??
A typical high-end SSD can sustain 100k write/erase cycles so you can
do some simple math to see that a 128GB device written to at a rate of
150M/s will last nearly 3 years. Again, note that unreliable devices
will result in a performance degradation when you fail a checksum in
the L2ARC, but the data will still be valid out of the main storage
pool.
You're going to see much more on this in the next few months. I made a
post to my blog that probably won't answer your questions directly, but
may help inform you about what we have in mind.
http://blogs.sun.com/ahl/entry/flash_hybrid_pools_and_future
Adam
--
Adam Leventhal, Fishworks http://blogs.sun.com/ahl
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
