There's a race condition that the dd can't account for. Think of a transaction in a database, where several records are part of a transaction. Each record gets written in turn, and then the transaction is committed.
What happens when the dd goes through that section of disk when only two of the four records have been written? Or one or more of those records are written to the area of disk already backed up, while others are written to a point that will soon be backed up? The image you get in the dd copy is inconsistent with the "real world" as the application views it, and so may not be useful when you have to restore it later. -- Robert P. Nix Mayo Foundation .~. RO-OC-1-18 200 First Street SW /V\ 507-284-0844 Rochester, MN 55905 /( )\ ----- ^^-^^ "In theory, theory and practice are the same, but in practice, theory and practice are different." On 8/16/10 9:49 AM, "McKown, John" <john.mck...@healthmarkets.com> wrote: > Wouldn't doing a "dd" in the running Linux guest to a separate disk, then > backing up that disk result in a good backup? Assuming that the application > has synced its data, of course. > > -- > John McKown > Systems Engineer IV > IT > > Administrative Services Group > > HealthMarkets(r) > > 9151 Boulevard 26 * N. Richland Hills * TX 76010 > (817) 255-3225 phone * (817)-691-6183 cell > john.mck...@healthmarkets.com * www.HealthMarkets.com > > Confidentiality Notice: This e-mail message may contain confidential or > proprietary information. If you are not the intended recipient, please contact > the sender by reply e-mail and destroy all copies of the original message. > HealthMarkets(r) is the brand name for products underwritten and issued by the > insurance subsidiaries of HealthMarkets, Inc. -The Chesapeake Life Insurance > Company(r), Mid-West National Life Insurance Company of TennesseeSM and The > MEGA Life and Health Insurance Company.SM > > > >> -----Original Message----- >> From: The IBM z/VM Operating System >> [mailto:ib...@listserv.uark.edu] On Behalf Of RPN01 >> Sent: Monday, August 16, 2010 9:47 AM >> To: IBMVM@LISTSERV.UARK.EDU >> Subject: Re: How to copy a disk using a z/Linux guest >> >> Flashcopy does not account for any disk buffers linux still >> has cached and >> unwritten. It will mitigate the situation where the disk is >> changing while >> it is being backed up. >> >> All in all, if you're talking about running images, full-pack >> backups are >> basically worthless. >> >> -- >> Robert P. Nix Mayo Foundation .~. >> RO-OC-1-18 200 First Street SW /V\ >> 507-284-0844 Rochester, MN 55905 /( )\ >> ----- ^^-^^ >> "In theory, theory and practice are the same, but >> in practice, theory and practice are different." >> >> >> >> On 8/16/10 9:38 AM, "Hans Rempel" <h...@hmrconsultants.com> wrote: >> >>> If you have flashcopy on your dasd that may be your best >> option. Use the >>> vmcp z/Linux module to invoke the FLASHCOPY command. >>> >>> Hans >>> >>> -----Original Message----- >>> From: The IBM z/VM Operating System >> [mailto:ib...@listserv.uark.edu] On >>> Behalf Of Rich Smrcina >>> Sent: August-16-10 9:37 AM >>> To: IBMVM@LISTSERV.UARK.EDU >>> Subject: Re: How to copy a disk using a z/Linux guest >>> >>> DDR won't care. It will take the VTOC with it. >>> >>> On 08/16/2010 08:29 AM, Martin, Terry R. (CMS/CTR) (CTR) wrote: >>>> >>>> Hi >>>> >>>> I am trying to find out if there is a utility in z/Linux >> in my case RHEL >>> 5.2 that will >>>> allow me to copy a z/Linux formatted disk to another disk. >>>> >>>> Also do you know if DDR cares rather there is a VTOC on a >> volume if it is >>> used to >>>> backup the volume without a VTOC? >>>> >>>> /Thank You,/ >>>> >>>> / / >>>> >>>> /Terry Martin/ >>>> >>>> /Lockheed Martin - Citic/ >>>> >>>> /z/OS and z/VM Performance Tuning and Operating Systems Support/ >>>> >>>> /Office - 443 348-2102/ >>>> >>>> /Cell - 443 632-4191/ >>>> >>>> / / >>>> >>>> /cid:image001.jpg@01C97FB5.5EAFD6C0/// >>>> >>> >> >>
