Date: Sun, 19 Feb 2012 00:55:04 +1000 From: Da Rock <freebsd-questions@herveybayaustralia.com.au> To: freebsd-questions@freebsd.org Subject: Re: /usr/home vs /home Message-ID: <4F3FBBC8.3030005@herveybayaustralia.com.au> In-Reply-To: <4F3FB5A0.9020806@infracaninophile.co.uk> References: <4F3ECF23.5000706@fisglobal.com> <20120217234623.cf7e169c.freebsd@edvax.de> <3D08D03C85ACFBB1ABCDC5DA@mac-pro.magehandbook.com> <alpine.BSF.2.00.1202172316230.11247@abbf.6qbyyneqvnyhc.pbz> <20120218112252.772c878b.freebsd@edvax.de> <4F3F80FD.8070201@herveybayaustralia.com.au> <4F3F8A46.1090908@infracaninophile.co.uk> <4F3F8D39.80907@herveybayaustralia.com.au> <4F3FA9FB.7030203@infracaninophile.co.uk> <4F3FAC17.8000300@herveybayaustralia.com.au> <4F3FB5A0.9020806@infracaninophile.co.uk>
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On 02/19/12 00:28, Matthew Seaman wrote: > 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. Thanks for the tips Matthew. Now you know why I haven't tackled that hurdle yet :) I'm gunna need some serious hardware...
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