Date: Tue, 15 Jan 2002 20:48:53 -0600 From: "Mike Meyer" <mwm-dated-1011581333.cbaae7@mired.org> To: Brian T.Schellenberger <bts@babbleon.org> Cc: questions@FreeBSD.ORG Subject: Re: HOWTO -- backup onto CDRs? Message-ID: <15428.59925.443917.666351@guru.mired.org> In-Reply-To: <0a2d11623021012FE4@mail4.nc.rr.com> References: <15426.33499.296182.78699@guru.mired.org> <200201152209.g0FM9eI00811@i8k.babbleon.org> <15428.54969.119254.138926@guru.mired.org> <0a2d11623021012FE4@mail4.nc.rr.com>
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Brian T. Schellenberger <bts@babbleon.org> types: > On Tuesday 15 January 2002 08:26 pm, Mike Meyer wrote: > > There's one other type of screwy file: sparse files. These have > > "holes" where there are no blocks on disk. You can create one > > trivially: > > Are these at all common? For the matter, are they preserved by cp? They > seem like a hyphothetical concern more than a practical one and a nuisance > more than a benefit. But maybe that's just me. Various implementations of db use them. The original implementation of UniCOS didn't provide them, and when we plugged in the db'ified version of the pwd routines and tried to make the password db, it ran root out of space. I'm not sure what else uses them, but the source for tar turn up a test for sparseness that ought to work on all Unix systems: if the stat structure's st_blocks times the file blocksize is less than the same structure's st_size. No, they aren't preserved by cp. Neither are flags, set*id bits, and a number of other things that one would rather not lose. If the cp crosses file systems, it also loses hard links. > Regardless, if you do a compressed backup they should compress real nicely > (though not as efficiently as the sparse files), though they will spring to > full space on a restore if the backup/restore program isn't clueful about > them. Springing back to full space can easily mean they don't fit on the restore media, even though it's bigger than the file system you are restoring. <mike -- Mike Meyer <mwm@mired.org> http://www.mired.org/home/mwm/ Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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