Logical Volume Manager (LVM) on LINUX (BALUG 2005-05-17 - P.S.)
Anyway, some items I could have covered a bit better at the 2005-05-17
presentation (some questions I didn't have complete/best answers to off
the top of my head, a trace of errata, some additional relevant
- "What is a meta device?"
- I did give a fair definition off the top of my head, but I find a much cleaner, handier one here (md(4) - at least with my distribution). In this context they're stating
"Multiple Device driver"
but md device file may be regarded as a meta device.
md - Multiple Device driver a.k.a. Linux Software Raid
The md driver provides virtual devices that are created
from one or more independant underlying devices. This
array of devices often contains redundancy, and hence the
acronym RAID which stands for a Redundant Array of Inde-
- Logical Volume (LV) - striping?
- I was asked about striping - but didn't have the answer off the top of my head (haven't had occasion to use that via LVM yet). Anyway, yes, LINUX LVM will do striping (see lvcreate (8)). Note also that LINUX has software RAID support, which includes striping (e.g. see mdadm(8), etc.).
- I was asked about lsvg - at the time, at least as far as I was able to quickly tell, that command doesn't exist in the LINUX implementation of LVM, and I believe I also said something to the effect that I wasn't aware of its existence in the HP-UX implementation of LVM either. With some subsequent searches on Google, it seems highly probable that lsvg is specific to the AIX (IBM's UNIX implementation) implementation of LVM, e.g.:
- LVM configuration files/data (other than what's on the Physical Volumes (PVs))?
- Other than /etc/lvmtab (which I gave only partial information on anyway), I wasn't, at the time of the presentation, able to exceedingly quickly point to specific files/locations on /etc where LVM data is stored. Anyway, lots more information on this can be found on various man pages, e.g.: vgcfgbackup(8), vgcfgrestore(8), and the -A or --autobackup option to many of the VG commands (e.g. vgcreate(8)), etc.
- growing and shrinking filesystems, online (mounted) and offline
- The number of filesystems that can be grown and shrunk offline, including those for LINUX, is sufficiently numerous I won't specifically address that (do note that perhaps some of them still can't be grown, and even more of them can't be shrunk - but many can).
- Online growing of filesystems - at least a couple support this, including but perhaps not limited to ext2/ext3 and reiserfs. They use somewhat different means/approaches for growing the filesystem (e.g. ext2online(8) vs. mount(8)). There's also the commercial Veritas filesystem (vxfs), which is also sold for LINUX. Beyond the LINUX realm, there are additional filesystem types that can be grown while online (e.g. Veritas vxfs (also appearing as HP-UX's Journaling File System (JFS)), ADvFS, ZFS - but see also the errata further below on ZFS).
- Online shrinking of filesystems - there's not a whole lot in this category.
There's the Veritas filesystem (vxfs) - a non-free commercial product - not to be confused with the free implementation - freevxfs.
Beyond the LINUX realm, there's ZFS (but also see errata further below),
Note that on-line shrinking of Veritas vxfs may not exactly be a "sliver bullet" - most notably it may frequently be unable to shrink a filesystem online, e.g.: Google Search: vxfs shrink "blocks in use". Due note that the Veritas filesystem shows up in many places., e.g. it is a commercial product available for many platforms, including LINUX, it also shows up in places such as HP-UX's JFS, among other places. Note also that in the case of HP-UX's JFS, the ability to shrink (or grow) online is bundled and priced as a separate product (OnlineJFS).
- After the presentation, I was asked about laptop model. The short (and incomplete) answer I gave was T40p (IBM ThinkPad), a more complete answer with full model number is: IBM ThinkPad T40p TYPE 2373-G1U. That data also happens to be within the notes (though a bit obscurely - it shows within an optional argument passed to XFree86(1) via startx(1)).
- Subsequent to the presentation, I found and corrected a typo in the notes, as noted on the html pages and screen shots pages.
- ZFS (Sun Microsystems Solaris)
- I was under the impression that ZFS shipped when Solaris 10 was originally released. At least based upon some bits of information I encountered, that appears not to be the case, e.g.:
- It was actually at the 2005-04-19 meeting, but someone asked me about laptop screen resolution, and I believe I rattled off an incorrect geometry (having very recently been seriously mucking about with XFree86 configuration stuff, thus having lots of geometries bouncing around in my head). Anyway, the correct answer (which I probably otherwise would have rattled off) is 1400x1050.