ZFS obn FreeBSD hardware model for 48 or 96 sata3 paths...

[Jason Usher]

--- On Sat, 9/17/11, Bob Friesenhahn <bfriesen at simple.dallas.tx.us> wrote:

> 150KB is a relatively small file size given that the
> default zfs blocksize is 128KB.  With so many files you
> should definitely max out RAM first before using SSDs as a
> l2arc.  It is important to recognize that the ARC cache
> is not populated until data has been read.  The cache
> does not help unless the data has been accessed several
> times. You will want to make sure that all metada and
> directories are cached in RAM.  Depending on how the
> files are used/accessed you might even want to intentionally
> disable caching of file data.


How does one make sure that all metadata and directories are cached in RAM?  Just run a 'find' on the filesystem, or a 'du' during the least busy time of day ?  Or is there a more elegant, or more direct way to read all of that in ?

Further, if this (small files, lots of them) dataset benefits a lot from having the metadata and dirs read in, how can I KEEP that data in the cache, but not cache the file data (as you suggest, above) ?

Can I explicitly cache metadata/dirs in RAM, and cache file data in L2ARC ?



> Are the writes expected to be synchronous writes, or are
> they asynchronous?  Are the writes expected to be
> primarily sequential (e.g. whole file), or is data
> accessed/updated in place?


It's a mix, I'm afraid.