error: build failed: committing transaction: disk I/O error

[Mark H Weaver <mhw@netris.org>]

In recent weeks on my system, it has become fairly common for the daemon
to get into a bad state, where all build attempts fail with messages
like this:

--8<---------------cut here---------------start------------->8---
mhw:~/guix-core-updates$ ./pre-inst-env guix build -n emacs
error (ignored): aborting transaction: cannot rollback - no transaction is active
guix build: error: build failed: committing transaction: disk I/O error
mhw:~/guix-core-updates$ 
--8<---------------cut here---------------end--------------->8---

Restarting 'guix-daemon' always fixes it, until the next time.  Note
that this happens on the master branch too, not just core-updates.  This
is on my MIPS system (YeeLoong 8101B with Loongson 2F CPU).  I'm not
sure if that's relevant.

Has anyone else seen this?

Unfortunately, I don't have a clear memory of what changes I made to my
system around the time this problem time began.  Possibilities include:

1. I switched to using Guix programs and libraries exclusively in my
   user session, and using them to build Guix itself, around that time.

2. I updated the upstream nix sources for the daemon around that time.

3. I switched to a modern version of Linux (3.13.x) around that time,
   which I'm pleased to report is now rock solid on my YeeLoong (uptime
   13 days so far, under continuous heavy load).

Any ideas?  When I get a chance, I'll attach 'strace' and/or 'gdb' to
the daemon and gather more info.

      Mark