On Mon, 08 Feb 2010 09:06 -0500, "Sean Kennedy" <[email protected]> wrote: > Moving this to m...@... > > Would part of this discussion usefully related to such issues like using > 'dd' > for diskwipes/copies/reformatting and slow data movement speeds? > > There are times when I am wiping (for reuse) hard disks using 'dd' and I > set > the BlockSize to > 512 (like 1M or so sometimes)
In my experience, a bs of 64k is about as big and fast as you'll get. Setting bs larger than that may make dd a tad faster, but not much. Also, when IO errors occur with a larger bs you'll drop more data than you would have using a 512 byte block. Some modified dd's, such as ddrescue, set larger blocksizes initially in an effort to increase speed, but revert to 512 bytes upon IO errors. Brad > and the transfer speeds are quite a lot slower than for using 'dd' on > some > other Operating systems. (Linux or Windows) > > Mind you, for a lot of this, I am using oBSD RamDISK, so I am not > anticipating > a full-fledged OS support for the ATA or SCSI or USB2 platforms. But for > those > systems where I am using -stable or -current, the speeds are still > comparably > slow. > > I concur with Theo's point on portability and making a sysctl for kernel > is > hazardous, but what am I seeing in the above for 'dd' that would be > causing > the poor performance? > (* BTW, I am using if=/dev/zero for the baseline, other if=/...'es may > have > lower performance as an input for compare*) > > > Just my 2 cents. > > -sean > > > Subject: Re: little cp diff > > 2010/2/8 Theo de Raadt <[email protected]>: > > > For those of you who asked why cp needs to be portable, come on. > > > You've got it all wrong. If cp isn't written in a portable fashion, > > > then what is the point of doing anything else in a portable fashion. > > This is good and reasonable answer. So I think we should stop discussion. > > antonvm
