On Tue, Nov 1, 2022 at 3:14 PM Roger Heflin <rogerhef...@gmail.com> wrote:
> I usually add a bs=4k or bs=16k or a bs=256k when using dd so the > blocksize is larger. That usually makes it quite a bit faster. fdisk shows block size > > > And if you background the dd you can use "vmstat 1" and the bi/bo > columns tell you the actual disk io rates, and you can use that to > reliably estimate. Elderly rescue CD’s have busybox, which provides nmeter. Fdisk gives values for logical and physical block size, but those may be fictional. % doas fdisk -l /dev/sdb1 Disk /dev/sdb1: 1.91 TiB, 2100425654272 bytes, 4102393856 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes On the elderly iMac, logical and physical were both 512. > > Default is 512 and does not align with most (all?) underlying physical > devices block sizes and may cause various layers extra work and take > much longer. > I have done experiments preparatory to using dd to clone a box of disks. Modern storage devices are more complicated and network speed means sneakernet is no longer needed. -- George N. White III
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