[volunteergrid2-l] Solving hardware problems with software

[Billy Earney]

Thanks for the info.. never heard of ATA over ethernet, so I've got some
reading to do!

-----Original Message-----
From: volunteergrid2-l-bounces at tahoe-lafs.org
[mailto:volunteergrid2-l-bounces at tahoe-lafs.org] On Behalf Of Shawn Willden
Sent: Wednesday, February 09, 2011 9:36 AM
To: a small group of people sharing storage resources with Tahoe-LAFS
Subject: [volunteergrid2-l] Solving hardware problems with software

This really has very little to do with the grid, but it's something I
thought was cool and that the folks on this list might appreciate.
It's about using ATA over Ethernet to solve disk connection problems.

My file server (which is the box that hosts my Tahoe nodes) has a
bunch of disks in it, all broken into small pieces with partitions,
when are then recombined in various ways in RAID arrays, which are
then pooled in LVM volumes, which are then carved out into logical
volumes for use.  All very complicated and very flexible.  I love it.

However, I find myself running low on disk space (not on the volumes
hosting Tahoe nodes, elsewhere), so I recently bought a 2 TB drive,
with the intention of replacing one of the existing 500 GB drives.
Doing the replacement involves temporarily adding the new drive in
addition to the existing drives (I could just yank-and-replace, but
that would result in my RAID arrays being degraded longer than
necessary).

So, to do that, I bought an inexpensive external drive adapter.  It
connects via either USB or eSATA and has a slot where you can
"hotplug" a SATA drive, either 3.5" or 2.5".  Very nifty, right?
Well... it turns out that my server has only USB1.1.  So when I
connected the drive via USB and started rebuilding an array with it,
it was sloooowww.  So slow that it was going to take me two weeks just
to get the new drive integrated, and during that entire time I'd have
at least one array degraded.  Not such a big deal for the RAID6
arrays, but degraded state leaves RAID5 very vulnerable.

So, I ordered a PCI card with an eSATA port.  That should be fast,
right?  Indeed it should.  Unfortunately, it didn't work at all.  The
card works; it has some internal ports which I'm using, but connecting
its external eSATA port to the adapter produces exactly nothing.  The
machine doesn't even recognize the drive's presence.

Finally, I remembered hearing something once about ATA over Ethernet.
 So, I found a tutorial, and it looked simple enough.  I installed the
2 TB drive in my desktop machine, and ran:

sudo aptitude install vblade
sudo modprobe aoe
sudo vblade 0 0 eth0 /dev/sdb

Then I ssh'd into my file server and ran:

sudo aptitude install aoe-tools
sudo modprobe aoe
sudo aoe_discover
sudo aoe_stat

... and I found I had access to a new, 2TB, AOE device!  Looking in
/dev/etherd I found that there were device nodes for each partition on
the device.  I proceeded to add one into a RAID array and start the
build process in motion.  Over Gig-E it's darned near as fast as if
the drive were installed in the file server, and it works like a
charm.

This isn't a long-term solution.  As soon as the RAID arrays have
integrated the new drive I'll shut the file server down, swap out the
now-unused 500 GB drive with the now-integrated 2 TB drive, and it
should start right up.

Anyway, the point of this whole thing is... Linux is cool :-)

-- 
Shawn
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