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The Open Source
Nicholas Petreley
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Scriptless spells disaster
MY LINUX-BASED VarLinux.org experienced a disk crash recently. Prior to this, I had equipped my server with two IBM model DTLA 46GB ATA-100 hard drives with SMART (Self-Monitoring Analysis and Reporting Technology); I had planned to use one for the live server and the other as a bootable backup of the system, which I had intended to update nightly using scheduled Linux shell scripts. Unfortunately, my brain is equipped with a procrastination feature called DUMB (Disasters Usually Motivate Backups), so I never wrote those scripts.
I know many people who practically worship these very same IBM drives, but I've experienced three failures so far with this model. Fortunately, the first two problems occurred before I had set up the server. By the time the second drive acted up, I had found out I could use Linux to create a bootable floppy with an IBM software utility called DFT (Drive Fitness Test), which restored the ailing drive well enough that it passed even the most strenuous tests. Everything ran smoothly for months when suddenly the main drive started reporting so many bad sectors on one partition that it refused to let me mount that partition. Luckily, the partition contained only the PHP code for the Web site, not the actual articles or user data.
I had been under the impression that most IDE drives automatically remap data as bad sectors develop. Unfortunately, SMART is only smart about monitoring and reporting problems. It's almost as DUMB as I am about preventing or fixing them. Even the DFT is too stupid to repair the drive without wiping out all your data.
I could use the utility to wipe and fix the drive, but I wanted to recover some data first. I couldn't mount the partition, so the prospect of recovering anything looked dim. I looked around for a Reiserfs utility that might help me recover something from that partition without having to mount it. Unfortunately, as good as Reiserfs may be, the maintenance utilities are terribly incomplete and poorly documented. Fortunately, Reiserfs is open source, which is what saved me. I scanned through the source code for the debugreiserfs program and was able to find some undocumented features in it that allowed me to recover some of the data from the faulty partition without having to mount it.
Once I had enough of a server to bring it back online, I created a mirror of it on the second drive. I swapped the master/slave jumpers on the drives to boot the good drive first, and then I planned to use DFT to wipe out the data on the bad drive to fix it. But before I took the leap, I tried mounting that bad partition again -- just for kicks. Not only did it mount properly, but all the data was there in perfect condition. Needless to say, I restored the previously lost data. And you can bet that I wrote those backup scripts immediately and deposited them in the /etc/cron.daily directory of my Debian Linux server, which ensures they'll run every night.
Nick is the founding editor of VarLinux.org ( www.varlinux.org ). Reach him at nicholas@petreley.com.
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