About Sir Santa's General Rule for Disk ... On Mon, Dec 21, 2009 at 22:02, Richard Troth <[email protected]> wrote: ... > General rule: use LVM and avoid partitioning *
I have to be careful when I say "avoid partitioning". If you use CDL, which is the default low-level formatting for ECKD DASD with 'dasdfmt', YOU MUST use partitioning. In all other cases (FBA, EDEV, "LDL" ECKD, IDE, SCSI, SATA) partitioning is not needed and may actually be counter productive. Even CD-ROM. Thumb drives too (if you don't need Windoze). So ... if you're NOT on CDL, avoid partitioning. By the way, there is no low-level formatting for FBA, EDEV, IDE, SCSI, SATA, ... or thumb drives ... or RAM. (There is for ECKD, whether CDL or LDL, and there is for CD-ROM.) If you think you need to partition a volume, consider instead feeding it to LVM as a PV and then letting LVM manage the slicing and dicing. Need more room in a "partition"? Do a quick 'lvextend'. Need more total space? Add more PVs! Partitioning is, and always has been, a crude form of filesystem below the "filesystems" we all know and love. It actually gets in the way of content sharing. And it doesn't grow past the one physical volume. You know how we share ECKD vols between VM LPARs? You can share SAN LUNs across systems, even different types of hardware and operating systems, if you avoid partitioning. The partition table *might* be recognized by the sharing OS, but it might not, and in any case it's one more thing to manage. Don't! Make life simple. The original question Martha asked had to do with SAN connectivity. Considering partitioning is relevant there. Want to do multipath? Coalesced paths are much more easily handled if you blow off partitioning. Want to copy content? You can use 'dd' most effectively where you're only after PV content or filesystem content. (Not likely that a CDL partition table will be worth much if you 'dd' it over to a SAN LUN.) This is not to say that there are not more opportunities for wonder and amazement. Surely there are myriad more ways we can obfuscate our data. It's just that partitioning is NOT one which I find effective anymore. -- R; <><
