Date: Thu, 7 Jun 2007 10:17:35 -0500 From: Brooks Davis <brooks@freebsd.org> To: Richard Noorlandt <lists.freebsd@gmail.com> Cc: freebsd-fs@freebsd.org Subject: Re: tunefs question Message-ID: <20070607151735.GA98301@lor.one-eyed-alien.net> In-Reply-To: <99c92b5f0706070804p42da0881kfc866b192be60ed5@mail.gmail.com> References: <99c92b5f0706070804p42da0881kfc866b192be60ed5@mail.gmail.com>
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--uAKRQypu60I7Lcqm Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Jun 07, 2007 at 05:04:09PM +0200, Richard Noorlandt wrote: > Hi everybody, >=20 > While reading a bit about tunefs I noticed that UFS reserves 8% of the d= rive > space for the root user and the system. However, I don't really understa= nd > what this space is actually used for. From the tunefs man page I underst= and > that it is primarily used to guard against fragmentation, and that's abo= ut > it. Is this the only thing that the reserved space is used for? >=20 > I'm building a large array for my fileserver, and it actually hurts a bi= t to > see that so much space is "wasted" without a very clear reason to do so. > Especially because the data on the array won't be modified very often, it > appears to be quite a lot of disk space just to prevent fragmentation. D= oes > anybody have some more information on this? >=20 > And while I'm at it: what is the effect of the expected average file size > option? What are the benefits and dangers of tweaking it? From the FreeB= SD > handbook I understand that the FS actually optimizes itself as time pass= es, > but that's about all that's said about it. The answer I've heard in the past is that the performance of the block allocation algorithms requires that most of the time an attempt to allocation from a cylinder group will succeed. If you reduce the free space too much that will not hold true anymore and thus your performance will suffer. 8% is actually a reduction from the historical 10%. In practice, the only way to decide what's right for your system is testing, but that's hard on a large system since it will take days to fill the disk. -- Brooks --uAKRQypu60I7Lcqm Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (FreeBSD) iD8DBQFGaCGPXY6L6fI4GtQRAoRDAJ9mU1veB2H4ilNGAZgNnyrCH0F8swCglWpo PIqaQsqQPgWjwKSp/Ke2o2I= =70yI -----END PGP SIGNATURE----- --uAKRQypu60I7Lcqm--
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