Date: Fri, 15 Sep 2000 12:14:49 +0100 From: Mark Ovens <marko@freebsd.org> To: Greg Lehey <grog@lemis.com> Cc: Dan Nelson <dnelson@emsphone.com>, Bruce Petro <bpetro@usa.com>, freebsd-questions <freebsd-questions@freebsd.org> Subject: Re: Compare FBSD File System Message-ID: <20000915121449.B257@parish> In-Reply-To: <20000915112618.L71517@wantadilla.lemis.com>; from grog@lemis.com on Fri, Sep 15, 2000 at 11:26:18AM %2B0930 References: <380327008.968949972194.JavaMail.root@web302-mc.mail.com> <20000914140402.A5897@dan.emsphone.com> <20000915112618.L71517@wantadilla.lemis.com>
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On Fri, Sep 15, 2000 at 11:26:18AM +0930, Greg Lehey wrote: > On Thursday, 14 September 2000 at 14:04:02 -0500, Dan Nelson wrote: > > In the last episode (Sep 14), Bruce Petro said: > >> Could someone shoot back a brief review of how the FBSD file system > >> compares to the old FAT system? General information is fine, but > >> please also cover: > >> > >> 1. Efficient Disk Usage - any min file size etc like fat? > > > > ffs has an 8k blocksize and a 1k fragment size. Small files and the > > ends of large files are put into fragments. > > You have a choice of block and frag size. Basically, > > 1. Frags must be a power of 2 and at least 512 bytes long. > 2. Blocks may contain 1 (I think), 2, 4 or 8 frags. > 3. Theoretically blocks may be any size within the above constraints, > but in practice you'd probably run into problems with blocks of > more than 64 kB. > 4. The larger the block size, the fewer inodes newfs reserves (though > you can override this choice). > Can you clarify the way these are actually used? AIUI, with 8KB blocks and 1KB frags, if a file is 8194 bytes (8KB + 2 bytes) the file will use one whole block and the extra 2 bytes will use 1 frag of another block. The remaining 1022 bytes of that frag will be unavailable to other files but the remaining 7 frags in the block will be (this is why FFS has less wasted space than FAT, which would make the remaining 8190 bytes in the block, cluster in FAT terminology, unavailable). Is this correct? Are the blocks which are used "by frag" in a special reserved area of the disk or can any block be used for this purpose as and when required and, if so, how does the system keep track of which frags in a block are in use? Is it meta-data stored in the directory entries or in the inode table perhaps? > In practice, you'd normally use either 4kB/512B for small files, or 8 > kB/1kB for larger files. > > >> 3. Any disk size limits? I believe I've seen some say there are > >> limits in the size disk you can use, but others seemed to reply > >> and say that that was old limits. > > > > There are always limits; I think the filesystem code has a 1TB > > filesystem-size limit, and you should be able to put a single 1TB > > file in that filesystem without any problems. > > I think the maximum file and file system sizes depend on the block > sizes. I think the 1 TB limit is for 8kB/1kB file systems. > > Greg > -- > When replying to this message, please copy the original recipients. > For more information, see http://www.lemis.com/questions.html > Finger grog@lemis.com for PGP public key > See complete headers for address and phone numbers > > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-questions" in the body of the message -- 4.4 - The number of the Beastie ________________________________________________________________ 51.44°N FreeBSD - The Power To Serve http://www.freebsd.org 2.057°W My Webpage http://ukug.uk.freebsd.org/~mark mailto:marko@freebsd.org http://www.radan.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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