Erik Trimble wrote:
Just a thought: would it be theoretically possible to designate some
device as a system-wide write cache for all FS writes? Not just ZFS,
but for everything... In a manner similar to which we currently use
extra RAM as a cache for FS read (and write, to a certain extent), it
would be really nice to be able to say that a NVRAM/Flash/etc. device
is the system-wide write cache, so that calls to fsync() and the like -
which currently force a flush of the RAM-resident buffers to disk -
would return as complete after the data was written to such a SSD (even
though it might not all be written to a HD yet).
Thoughts? How difficult would this be? And, problems ? (the biggest I
can see is for Flash, which, if it is being constantly written two, will
wear out relatively quickly...)
The product was called Sun PrestoServ. It was successful for benchmarking
and such, but unsuccessful in the market because:
+ when there is a failure, your data is spread across multiple
fault domains
+ it is not clusterable, which is often a requirement for data
centers
+ it used a battery, so you had to deal with physical battery
replacement and all of the associated battery problems
+ it had yet another device driver, so integration was a pain
Google for it and you'll see all sorts of historical perspective.
-- richard
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