hi ed my understanding .. - most ( 99% ) of disk ascess is done by "device drivers" that writes/reads in 512bytes ( sectors ) - the device drivers knows where allthe bad blocks are - when using tar, and any other app to write data, the file is written and avoids the 'bad blocks" - dd on the other hand, is a bit-level copy, that includes copying of "partition" info to the next drive... which drags along the bad block data ... dd if=/dev/hda of=/dev/hdb ( everything including partitions is copied over ) - but given todays manufacturing technology of disk drive platters, i think most people have forgetten about "bad blocks" - most people also do NOT use "check for bad block option" on their 40GB or 6)GB or 100GB drive which can takes 6-10 hrs even on a 1GHz machine - not sure what will happen if one didnt do "bad block checking" during formatting right after fdisk'ing - i think, one day, someone will lose a block of data on that one bad block that happen to be bad - most apps does NOT write data and read it back ?? - that was the job of mke2fsck to format the drive and check it - writes to disk can be 2x faster(?) if it wasnt "verifying" ( just asume that the disk controller knows what to do, as opposed ( to the application code that writes user data to the disks anyway.. so goes my limited understanding ... tar(block/sector level apps ) vs dd(bit level apps ) type of apps c ya alvin On Sun, 13 Oct 2002, Ed Carp wrote: > > -- most people assume that there is no bad block on the disks > > when using DD to copy data > > - if there is a bad block on the master, you copy > > that to the clone > > Not true. IDE drives transparently remap bad sectors, so you'll not see a bad sector on an IDE drive unless the remap area is full, > then the drive is toast anyway. > > Regardless, the disk driver will return an error to the application program if there is an error reading data, so it is not possible > to copy a bad sector from one disk to another. > -- > Ed Carp, N7EKG http://www.pobox.com/~erc 214/986-5870 > Licensed Texas Peace Officer > Computer Crime Investigation Consultant > > Director, Software Development > Escapade Server-Side Scripting Engine Development Team > Pensacola - Dallas - London - Dresden > http://www.squishedmosquito.com > > "The whole aim of practical politics is to keep the populace alarmed-- and > thus clamorous to be led to safety-- by menacing it with an endless series > of hobgoblins, all of them imaginary." > -- H. L. Mencken > ----------------------------------------------------------------- This list is provided by the SecurityFocus ARIS analyzer service. For more information on this free incident handling, management and tracking system please see: http://aris.securityfocus.com
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