I have two backup drive, keeping one off-site and swapping them every week or two. I did a swap yesterday, mounted the drive on my MBP and backed it up, then switched it to my iMac and backed that up. Both backups were uneventful and successful. (I normally leave the drive attached to the iMac and backup the MBP over the network, but usually do the first backup and a verify attached to the MBP when I swap drives because the MBP has USB3 and is faster. I didn't do the verify this time.)

This morning, today's (network) backup of the MBP failed showing "size of negative hash map not power of 2" and " A network or disk error was encountered." Those errors also showed up when I tried to backup the iMac (directly mounted) and when I try to backup the MBP with the drive mounted there. I get the same errors when I attempt to do a verify.

Disk Utility and TechTool Pro both show the drive as being OK. I've started a repair and that seems to be proceeding normally, but I wanted to let you know about this behavior in any case. I'll send a report from the MBP; if you'd also like one from the iMac let me know.

Ralph Strauch wrote:This morning, today's (network) backup of the MBP failed showing "size of negative hash map not power of 2" and " A network or disk error was encountered."

That's a very unusual error. If I had to guess, I'd say that something went wrong as the archive was being closed. The negative map is only resized a few times during the lifetime of the archive, and its length is always a power of 2. So for something to change that is unusual.

(I've learned that all software has bugs, even filesystem software. Something things just don't happen the way they should.)

Those errors also showed up when I tried to backup the iMac (directly mounted) and when I try to backup the MBP with the drive mounted there. I get the same errors when I attempt to do a verify.

That's correct. Every time the archive is opened, QRecall performs some basic sanity checks. QRecall will refuse to use the archive until this problem is corrected.

I've now completed a repair and it seems to be acting normally again.

Thanks.