I'm trying to add error correction to one of my backup drives I?m getting ?insufficient space? errors. The archive is 1.23tb, drive has 197gb free, and I?m using 1:8 redundancy. The first time it happened I had just cleaned some files off the drive and though maybe qrecall hadn't updated it reading of the drive, so I quit qrecall and restarted it, Same result.

I installed error correction on my other backup drive yesterday an it went smoothly.
I've filed a report.

Filling up a volume, completely, is a nasty situation in OS X (a.k.a. BSD Unix). Because of this, QRecall reserves a 4% buffer when estimating the amount of free space on your drive.

So the volume with your 1.23 TB archive has 197 GB of free space. Assuming the archive is just about the only thing on the volume, that works out to about 3% free space. As far as QRecall is concerned, your drive is already full.

To add 1:8 redundancy to at 1.23 TB archive, QRecall will want to see 154 GB (1/8th of 1.23 TB) + 4% of the volume size (~50 GB), or at least 204 GB of free space before it will proceed.

OK, Thanks for that explanation. I knew that OSX needed a fair amount of headroom on boot disk for OS functions, but had just assumed that no headroom was needed on an external data disk. It's good to have that misperception corrected.

The startup filesystem needs headroom for things like swap and temporary files. If you completely run out of space on the VM swap volume, you are in serious doo-doo...

But even non-boot filesystems start to hurt as their free space dwindles towards zero. The problem is the volume's allocation map. As the drive fills up, it's harder and harder of the filesystem to find free blocks, and those blocks become increasingly smaller and more fragmented. Eventually, the filesystem slows to a crawl trying to find and manage the free space. You can improve this by defragmenting the drive, but when it's nearly full even that becomes problematic.

Because of this, and other reasons, QRecall avoids letting the archive volume fill up completely. The capture action monitors the free disk space and will stop capturing when the volume exceeds approximately 98% full. (The actual amount is variable, based on the size of the volume.)