Blog O’ Matty

I use the MD (multiple device) logical volume manager to mirror the boot devices on the Linux servers I support. When I first started using MD, the mdadm utility was not available to manage and monitor MD devices. Since disk failures are relatively common in large shops, I used the shell script from my SysAdmin article Monitoring and Managing Linux Software RAID to send E-mail when a device entered the failed state. While reading through the mdadm(8) manual page, I came across the “–monitor” and “–mail” options. These options can be used to monitor the operational state of the MD devices in a server, and generate E-mail notifications if a problem is detected. E-mail notification support can be enabled by running mdadm with the “–monitor” option to monitor devices, the “–daemonise” option to create a daemon process, and the “–mail” option to generate E-mail:

$ /sbin/mdadm –monitor –scan –daemonise –mail=root@localhost

Once mdadm is daemonized, an E-mail similar to the following will be sent each time a failure is detected:

From: mdadm monitoring 
To: root@localhost.localdomain
Subject: Fail event on /dev/md1:biscuit

This is an automatically generated mail message from mdadm
running on biscuit

A Fail event had been detected on md device /dev/md1.

Faithfully yours, etc.

I digs me some mdadm!

While attempting to create a 2-way LVM mirror this weekend on my Fedora Core 5 workstation, I received the following error:

$ lvcreate -L1024 -m 1 vgdata

  Not enough PVs with free space available for parallel allocation.
  Consider --alloc anywhere if desperate.

Since the two devices were initialized specifically for this purpose and contained no other data, I was confused by this error message. After scouring Google for answers, I found a post that indicated that I needed a log LV for this to work, and the log LV had to be on it’s own disk. I am not sure about most people, but who on earth orders a box with three disks? Ugh!