Date: Sat, 18 Feb 2012 14:28:48 +0000 From: Matthew Seaman <m.seaman@infracaninophile.co.uk> To: freebsd-questions@freebsd.org Subject: Re: /usr/home vs /home Message-ID: <4F3FB5A0.9020806@infracaninophile.co.uk> In-Reply-To: <4F3FAC17.8000300@herveybayaustralia.com.au> 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>
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This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigE7D6FF520B8D0D9E72B352D1 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On 18/02/2012 13:48, Da Rock wrote: > I was thinking along the lines of continuous heavy load of writing (som= e > 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. >=20 > 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 writte= n > 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. >=20 > Now you see how a terabyte and a half disk space can be used in a matte= r > 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 --=20 Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard Flat 3 PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate JID: matthew@infracaninophile.co.uk Kent, CT11 9PW --------------enigE7D6FF520B8D0D9E72B352D1 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG/MacGPG2 v2.0.16 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAk8/tagACgkQ8Mjk52CukIyzSwCeMrCEsqWRRxcne511oFp6vK8+ WfYAnjz5q74sXTSsaO0qW4PNAn4dPceM =HbCD -----END PGP SIGNATURE----- --------------enigE7D6FF520B8D0D9E72B352D1--
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