/usr/home vs /home

[Matthew Seaman]

On 18/02/2012 13:48, Da Rock wrote:
> I was thinking along the lines of continuous heavy load of writing (some
> read) rather large files (5G+ would be average - multiple!) - does that
> warrant caching or is it only lots of smaller files? That and lots of
> ~0.5G files (read mostly) is what defines the main load on the system.
> 
> I ask because I'm not 100% sure of what the caching is for. I had
> thought it was like the journal log for fast writing to be later written
> to the filesystem itself, but now I think I may be wrong in my
> judgement. It now sounds like a fast access for usual suspects.
> 
> Now you see how a terabyte and a half disk space can be used in a matter
> of hours :)

Right.  That's a lot more file IO than I anticipated in my previous
answer.  For that amount of usage, 8GB would definitely be required and
quite possibly more.  Separate devices for ZIL and ARC would be a good
idea.  (ZIL is effectively the caching for the write path, ARC for the
read path.  That's a gross over-simplification actually, but good enough.)

The caching is vital -- it's where all the stuff like checking the
parity for a RAIDZn device happens, or the compression/decompression
actions.  Yes, it works like file system journalling too.

	Cheers,

	Matthew

-- 
Dr Matthew J Seaman MA, D.Phil.                   7 Priory Courtyard
                                                  Flat 3
PGP: http://www.infracaninophile.co.uk/pgpkey     Ramsgate
JID: matthew at infracaninophile.co.uk               Kent, CT11 9PW

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