dinah@shell.com (Dinah Anderson) (06/30/89)
We have several 1 gb disk drives and it does not make a whole lot of sense
to reserve 100 mb (10%) for space threshold. Has anyone reduced this
number and if so to what percentage and what are the consequences of doing
so? Thanks.
Dinah Anderson
Shell Oil Company, Information Center (713) 795-3287
..!{sun,psuvax,bcm,rice}!shell!dinahlad@uunet.uu.net (lad) (07/11/89)
> From article <4243@kalliope.rice.edu>, by dinah@shell.com (Dinah Anderson): > We have several 1 gb disk drives and it does not make a whole lot of sense > to reserve 100 mb (10%) for space threshold. Has anyone reduced this > number and if so to what percentage and what are the consequences of doing > so? Thanks. > > Dinah Anderson I have recently used the -m option to reserve half of the normal 10% on 2 of our 892 MB disks. We've only been running on these disks for about a month, but so far I haven't been sorry I did it. Instead of losing 88MB to free space I picked up about 45MB extra space on the disk. Since we do not run quotas I don't ever see this being a problem. Lawrence A. Deleski | Silicon Compiler Systems uunet!sdl!lad | 15 Independence Blvd. Cash-We-Serve 76127,104 | Warren, NJ 07060 MABELL: (201) 580-0102 | Ext. 283
henry@uunet.uu.net (Henry Spencer) (07/12/89)
>We have several 1 gb disk drives and it does not make a whole lot of sense >to reserve 100 mb (10%) for space threshold... Unfortunately it does continue to make sense. It's not a matter of having some reserve for emergencies (in which case reducing the reserve on a big disk would indeed make sense). The issue is that filesystems which try to keep the blocks of a file together, a la 4.2BSD and successors, lose performance badly if they get quite full. To have a reasonable chance of finding empty blocks near the right place for a new file, the filesystem has to have a certain "density" of empty blocks, be the filesystem one meg or a thousand. The constant percentage is indeed the right approach. It's part of the price paid for performance. Now, there are some caveats to this. First, you have to believe that keeping the blocks together is a win. It definitely is on a single-user machine; how much it helps on a timesharing system or a server is a very good question that (as far as I know) has never been systematically looked at. (All those impressive 4.2BSD filesystem benchmarks were run single-user, and multi-user comparisons seldom make any attempt to separate the effects of better block placement from the obvious win of bigger blocks.) Second, you have to be using the filesystem to hold lots of little files that come and go, rather than a few monsters that just sit there. And third, whether 10% is the right percentage is open to debate, and is perhaps somewhat site-specific. I believe people have cut it to 5% with no major ill effects. Henry Spencer at U of Toronto Zoology uunet!attcan!utzoo!henry henry@zoo.toronto.edu
poffen@sj.ate.slb.com (R. Poffenberger) (07/31/89)
>I have recently used the -m option to reserve half of the normal 10% on 2 >of our 892 MB disks. We've only been running on these disks for about a >month, but so far I haven't been sorry I did it. Instead of losing 88MB >to free space I picked up about 45MB extra space on the disk. Since we do >not run quotas I don't ever see this being a problem. You might want to check on the -o option if you use -m. By using -m to set the free space to less than 10%, the filesystem is optimized for disk space usage by default. If 10% or greater, the file system is optimized for speed. You can override these defaults using -o. R. Poffenberger poffen@sj.ate.slb.com Schlumberger Technologies ATE division. ...In a dictatorship, people siffer without complaining, In a democracy, people complain without suffering.