/usr/bin/file rules, even when it’s wrong

Posted by max on July 11, 2008

‘file’ is a great utility. Even when it’s wrong, it can at least be good for an audible laugh:

$ dd if=/dev/urandom of=fakefile.bullshit bs=4096 count=400
400+0 records in
400+0 records out
1638400 bytes (1.6 MB) copied, 0.307462 s, 5.3 MB/s
$ file fakefile.bullshit
fakefile.bullshit: DOS executable (COM)

Popularity: 57% [?]

How to learn (and not get burned by) LVM

Posted by max on July 02, 2008

LVM2 is a very useful thingy indeed. I sort of misunderstood its utility for a while. It’s not just for managing storage on mongo SAN clusters; it can be very useful for managing storage on a workgroup box with several drives.

However, on Linux, beware: You cannot boot from an LVM logical volume. You need to have a regular filesystem (ext2/ext3/xfs/jfs/reiserfs/etc.) partition for /boot. I’m not quite sure why I didn’t grasp this when planning my first LVM layout.

The Red Hat documentation on LVM2 is excellent, but is not the first thing that comes up on searches, because it’s buried in the weirdo RHEL system documentation. There’s a similar, RedHat-generated doc which is also good at the CentOS project, available here.

It takes some getting used to to understand LVM, and if you’re like me, it doesn’t hurt to practice. There is some degree of overlap with what RAID can do for you, and using them both together makes one’s head spin at first. Drawing a map of your planned layout is extremely helpful.

For wrangling your storage layouts, the Parted Magic live CD can be very helpful. Unfortunately, not all installers want to respect what you’ve laid out with it. Fedora 9 played nice. Ubuntu 8.10 (alternate install CD — essential for RAID installs) was not; it kept not respecting the /dev/md software RAID devices that I’d previously set up, then would create some new bogus md devices.

Popularity: 59% [?]