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Full Discussion: dd command
Operating Systems Solaris dd command Post 99966 by Perderabo on Wednesday 22nd of February 2006 04:39:10 PM
Old 02-22-2006
Some day I will benchmark a few runs of dd and find the optimal setting, if there is one. I have only dd'ed magnetic disks. Never dd'ed a cd-rom, let alone a dvd. So I'll stay with what I know. Use the rdsk style device, not the dsk so the data goes to straight your data segment (not via the buffer cache). The rdsk driver has to read whole sectors. If you ask for a piece of a sector, it may not work. Or it may read a sector and discard what you don't want. I stay with a multiple of 1024. Bigger is better than tiny. But after a point, the advantage starts to taper off. 1 MB is the smallest size I would consider trying. I will want to mentally estimate how much is left, etc...so no screwball sizes. I wind up with N * (1 MB) where N is some small integer. 10 MB seems like a nice round number. We have one bad spot on the disk. I expect dd to fail when it gets there. I will restart it on the next 10 MB chunk. So I have doomed myself to having a 10 MB hole in my disk. That is pretty much my thought process as I picked my blocksize.

It would be a disaster to pick a buffer size so large that box starts to page. I have plenty of memory on this box, so no problem there.
 

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DISKPART(8)						    BSD System Manager's Manual 					       DISKPART(8)

NAME
diskpart -- calculate default disk partition sizes SYNOPSIS
diskpart [-d] [-p] [-s size] disk-type DESCRIPTION
diskpart is used to calculate the disk partition sizes based on the default rules used at Berkeley. Available options and operands: -d An entry suitable for inclusion in the disk description file /etc/disktab is generated; for example, disktab(5). -p Tables suitable for inclusion in a device driver are produced. -s size The size of the disk may be limited to size with the -s option. On disks that use bad144(8) type of bad-sector forwarding, space is normally left in the last partition on the disk for a bad sector forward- ing table, although this space is not reflected in the tables produced. The space reserved is one track for the replicated copies of the ta- ble and sufficient tracks to hold a pool of 126 sectors to which bad sectors are mapped. For more information, see bad144(8). The -s option is intended for other controllers which reserve some space at the end of the disk for bad-sector replacements or other control areas, even if not a multiple of cylinders. The disk partition sizes are based on the total amount of space on the disk as given in the table below (all values are supplied in units of sectors). The 'c' partition is, by convention, used to access the entire physical disk. The device driver tables include the space reserved for the bad sector forwarding table in the 'c' partition; those used in the disktab and default formats exclude reserved tracks. In normal operation, either the 'g' partition is used, or the 'd', 'e', and 'f' partitions are used. The 'g' and 'f' partitions are variable-sized, occupying whatever space remains after allocation of the fixed sized partitions. If the disk is smaller than 20 Megabytes, then diskpart aborts with the message ``disk too small, calculate by hand''. Partition 20-60 MB 61-205 MB 206-355 MB 356+ MB a 15884 15884 15884 15884 b 10032 33440 33440 66880 d 15884 15884 15884 15884 e unused 55936 55936 307200 h unused unused 291346 291346 If an unknown disk type is specified, diskpart will prompt for the required disk geometry information. SEE ALSO
disktab(5), bad144(8) HISTORY
The diskpart command appeared in 4.2BSD. BUGS
Most default partition sizes are based on historical artifacts (like the RP06), and may result in unsatisfactory layouts. When using the -d flag, alternative disk names are not included in the output. BSD
June 6, 1993 BSD
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