Date: Sun, 30 Jan 2005 23:24:37 +0100 From: "Poul-Henning Kamp" <phk@phk.freebsd.dk> To: Ulrich Spoerlein <q@uni.de> Cc: freebsd-stable@freebsd.org Subject: Re: Size of metadata required for GBDE Message-ID: <76988.1107123877@critter.freebsd.dk> In-Reply-To: Your message of "Sun, 30 Jan 2005 23:18:03 %2B0100." <20050130221803.GB2600@galgenberg.net>
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In message <20050130221803.GB2600@galgenberg.net>, Ulrich Spoerlein writes: >Hi all, > >I just fiddled around with using GBDE for ISO images (it works) and >stumbled across the need to "guess" the size required for the GBDE >container. > >Looks like the size is not increasing linearly. Here are the numbers of >512 byte blocks available in md0 and md0.bde > md0 | md0.bde | diff. > 2048 1952 96 > 4096 3936 160 > 8192 7936 256 >16384 15872 512 >32768 31744 1024 >65536 63520 2016 > >So, what's the correct formula? First off, if you want to use gbde on a CDROM you should use a sectorsize of 2048 througout (-S 2048 argument to mdconfig). The amount of metadata in GBDE is pretty straight forward: 1. If do not use off-line keyfiles: deduct one sector. 2. Deduct the key sectors (1 to 4) 3. Find zone size: nsect = sectorsize / 16 nzone = nsect + 1 4. Find number of zones: z = remaining_sectors / nzone 5. Find usable size: size = z * nsect 6. Find overhead/metadata as: total_sectors - size -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.
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