Date: Fri, 26 May 1995 09:06:30 +1000 From: Bruce Evans <bde@zeta.org.au> To: cs.weber.edu!terry@sbstark.cs.sunysb.edu, gene@starkhome.cs.sunysb.edu Cc: FreeBSD.org!current@sbstark.cs.sunysb.edu, blaise.ibp.fr!roberto@sbstark.cs.sunysb.edu, phk@ref.tfs.com Subject: Re: newfs weirdness... Message-ID: <199505252306.JAA11068@godzilla.zeta.org.au>
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>In the absence of information to the contrary, for an IDE drive it seems >to me that the best available information is that which is supplied by the >drive. Barring that, what is in the disklabel is next best. I can't >possibly see why a 4096/1 geometry is going to be uniformly better than >these other choices. Plus you have to go to extra trouble to avoid >wasting sectors and getting the warning message. It's better because 4096 is larger than the average fake cylinder. (This will probably change when disks get larger - all disks will have 1024 heads, 256 sectors and 63 sectors; larger disks will be unstriped and everyone will complain about the 8GB limit :-]). Sectors on the fake cylinder after the last full fake cylinder (if any) are wasted anyway. The standard seems to be to not document such sectors for IDE, but you may be able to use them by picking a different geometry or by setting the partition table and labels to cover them. Using the 4096/1 geometry increases the wastage: - if 4096 is large, then the average wastage is larger. - if the original fake cylinder size is not a divisor of 4096, then rounding twice to a fake cylinder boundary increases the wastage - the original fake cylinder size may be chosen to be minimise the wastage. This is likely iff it is not a divisior of 4096. Bruce
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