Backing up and cloning AIX: mksysb, savevg, and low-risk upgrades with alt_disk_copy

Goal

Take a restorable backup of an AIX system's rootvg, confirm what a mksysb image contains without restoring it, and perform a Technology Level update with a same-system fallback instead of relying solely on restoring from tape.

Prerequisites

Root access; enough space on the target media (tape device, NIM server file, or local disk) for the full rootvg content; for alt_disk_copy, an additional unused disk visible to lspv.

Steps

mksysb backup

1. Create the backup: mksysb -i /dev/rmt0 (to tape) or to a file on a NIM server; mksysb backs up all mounted JFS/JFS2 data in rootvg plus enough information to reinstall the base operating system.
2. If the image may later seed a different machine, plan to answer "no" to the restore-time "recover devices" prompt so the target's own device tree is (re)discovered instead of the source machine's.
3. To back up a non-rootvg volume group instead, use savevg -i -f <device-or-file> <vgname>; the image is not bootable and is restored onto a running system with restvg.

Verifying a mksysb without restoring it

4. Run lsmksysb against the image to inspect it non-destructively (for example lsmksysb -lf <image-file>): it can show the lslpp -L-equivalent list of filesets installed on that rootvg, and lsvg-equivalent volume group and size information, including the size the backup would occupy if restored at minimum size.

Low-risk upgrade with alt_disk_copy

5. Identify a spare disk with lspv (volume group column None). None only means no AIX volume group is active on it: confirm it is not a raw device used by a database or a SAN LUN shared with another LPAR, because the next step overwrites it.
6. Clone the running rootvg onto it: alt_disk_copy -BOd hdiskX — -B leaves the current bootlist pointing at the original disk, and -O resets the copy's device-specific ODM entries so it will not conflict if it is ever moved to different hardware.
7. To combine cloning with an update in one step, add the update flags to the clone, for example alt_disk_copy -d hdiskX -b update_all -l <lpp_source-directory>; the running rootvg stays untouched. (alt_disk_mksysb is the related command that installs an existing mksysb image onto a spare disk, with -O for a device reset.)
8. Boot from the alternate disk (via bootlist or an HMC-selected boot device) to test the updated copy; if it fails, switch the bootlist back to the untouched original disk (or pick it from the SMS boot menu if the clone does not come up) — no restore required.

Expected result

A verified mksysb/savevg image exists off-system; lsmksysb confirms its fileset and volume group content; an alt_disk_copy clone boots independently of the original disk, giving a same-day fallback path.

Limits and test basis

This describes rootvg duplication only; other data volume groups need savevg/restvg or their own plan. Duplicating rootvg by a bitwise disk copy or by moving physical disks between systems is not among IBM's supported methods: with directly attached disks the copy may not boot (LED 554), because hardware-specific ODM data (location codes, WWPNs) will not match the new hardware.