On Sat, Jul 06, 2002 at 05:33:50PM -0700, Matthew Dillon wrote: > > : > :On Sat, Jul 06, 2002 at 04:42:22PM -0700, Matthew Dillon wrote: > :> Negative block numbers are used by UFS to represent the indirect blocks > :> associated with a file, while positive block numbers represent the > :> contents of the file. > : > :I never saw any negative block numbers in on-disc structures. > :Now I wonder if it was just hidden behind macros. > :What is the reason to handle it that way? > :Do you have some code reference for homework? > > LOGICAL block numbers, not physical block numbers.
ufs on disc structures are using logical block numbers. But well I've already found what you mean. > :> These are logical block numbers, which are fragment-sized (1K typically). > :> So, 2^31 x 1K = 2TB. > :> > :> Physical block numbers are 512-byte sized, with a range of 2^32 > :> in -stable. This also winds up being 2TB. So increasing the fragment > :> size does not help in -stable. > : > :It's a proven fact that there is a 1T limit somewhere which was > :explained with physical block numbers beeing signed. > > test1# vnconfig -e -s labels -r reserve -S 2t vn0 > test1# disklabel -r -w vn0 auto > test1# disklabel vn0 > ... > bytes/sector: 4096 > ... > 8 partitions: > # size offset fstype [fsize bsize bps/cpg] > c: 536870912 0 unused 0 0 # (Cyl. 0 - 2097151) > > Theoretically VN can create up to an 8TB virtual disk because the > sector size for a swap-backed VN device is 4K, but I'm not sure I > would want to test the theory. > > > With a regular file: > > test1# vnconfig -e -s labels -T -S 2047g vn0 test.dat > test1# disklabel -r -w vn0 auto > test1# disklabel vn0 > ... > bytes/sector: 512 > ... > c: 4292870144 0 unused 0 0 # (Cyl. 0 - 2 > > test1# ls -la test.dat > -rw---xr-- 1 root wheel 2199023255552 Jul 7 00:31 test.dat > test1# > > (of course, god help you if you tried to 'newfs' the above!) But that's the important point. You can happily create vinum 2T volumes but you can never newfs them, because daddr_t, which is used in struct buf, is signed. This case was tested using real disks. OK you can format a disk using 1k sectors. But I was told that vm internaly always adapts to 512 byte blocks using signed 32bit varables so it wouldn't help. -- B.Walter COSMO-Project http://www.cosmo-project.de [EMAIL PROTECTED] Usergroup [EMAIL PROTECTED] To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-hackers" in the body of the message
