Date: Thu, 27 May 1999 07:15:56 -0700 From: Don Lewis <Don.Lewis@tsc.tdk.com> To: Graeme Tait <graeme@echidna.com> Cc: freebsd-hackers@FreeBSD.ORG, info@boatbooks.com Subject: Re: File system gets too fragmented ??? Message-ID: <199905271415.HAA10721@salsa.gv.tsc.tdk.com> In-Reply-To: Graeme Tait <graeme@echidna.com> "Re: File system gets too fragmented ???" (May 27, 5:07am)
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On May 27, 5:07am, Graeme Tait wrote: } Subject: Re: File system gets too fragmented ??? } I've received several answers along this direction, but I want to emphasize one } point that I think is being overlooked. When the filesystem is fresh and a new } archive is expanded to create ~900,000 small files each of 2-5 512 byte frags } in size, the filesystem appears quite well-behaved, and space seems to be } efficiently utilized. } } The problem seems to be that with successive updates that slightly change the } size of files, or add or delete files, that a large number of unallocated } fragments are created. } } I don't understand how the FFS stores files of sub-block size. Do the fragments } used need to be contiguous, or entirely within a single block? Yes and yes. } The choice of 512 byte frags is based on average wastage per file of half a } frag, or about 230MB with 900,000 files. It's quite possible that a 2k frag/16k } blocksize would improve utilization of fragments, as the vast majority of files } would then fit in a single fragment, but in this case there would be of order } 800MB wastage, and the files would not fit the existing disk. You might try unmounting the filesystem and doing tunefs -o space /dev/rawdevice (which can also be done at newfs time). You may find that the performance, especially write performance, isn't too good. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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