On Mar 7, 2011, at 1:58 AM, Markus Hitter wrote:
> > Am 06.03.2011 um 15:28 schrieb Ashley Aitken: > >> I could not use Disk Utility to do a block copy of this disk (for some >> reason it would stop and hang the app or machine part way through). This >> was during the hot period and the disk could have been overheating during >> the operation > > If the disk is subject to overheating, get it cooled. Often this is a simple > as unmounting it from the housing and let it dangling in fresh air. Not a > long term solution, of course, but totally sufficient for doing a copy. > Cooling a disk usually usually makes it operational again. > > Copying the raw device with "dd" is a good idea, as this reduces reading head > movement to a minimum. IIRC, copying a raw device to a file gives you > something you can convert with diskutil to a valid DMG. Please don't nail me > down to the details, it's quite some time since I've done that last time. > > If the disk still overheats, you can use "dd" to copy in smaller chunks. Read > 10 MB, sleep a second, repeat. Takes some time, but gives reliable results. > > In the worst case, you have to instruct "dd" to fill sectors with read > failure with zeroes. So you loose only a few single sectors instead of entire > files. Beware, "dd" simply drops sectors with read failure by default, making > the copy useless. But there are switches to avoid that. See thread "Mac OS vs Fedora disk performance" I am seeing a HUGE difference in dd performance between the block device /dev/disk0 and the raw device /dev/rdisk0. I know using something like: dd if=/dev/disk0 of=/dev/disk1s2/diskimages/imageofhotharddrive.iso bs=256k will produce a valid ISO that you can mount and traverse the files. It will contain the full partition map, directory, everything. I have not tried using the raw device: dd if=/dev/rdisk0 of=/dev/disk1s2/diskimages/imageofhotharddrive.iso bs=256k This would be 6x faster on my machine, but I don't know the difference with XNU between block level and raw device other than performance. Obviously I would prefer to use rdisk because it is way faster. But I don't know what the result is. I like the idea of yanking the drive, letting it hang out, and doing a dd with the raw /dev/rdiskX and then inspecting the resulting iso. If it even mounts and is navigable, you're set, although you could try launching an executable to be sure - or using md5 on two files to ensure they're identical. It's a sector copy so I don't see why they would not be. If it turns out it's not usable, then you could revert to the block level /dev/diskX and retry...worth trying to go faster than slower. Chris Murphy_______________________________________________ MacOSX-admin mailing list [email protected] http://www.omnigroup.com/mailman/listinfo/macosx-admin
