HAMMER2 emergency space mode

As anyone who has been running HAMMER1 or HAMMER2 has noticed, snapshots and copy on write and infinite history can eat a lot of disk space, even if the actual file volume isn’t changing much.  There’s now an ‘emergency mode‘ for HAMMER2, where disk operations can happen even if there isn’t space for the normal history activity.  It’s dangerous, in that the normal protections against data loss if power is cut go away, and snapshots created while in this mode will be mangled.  So definitely don’t leave it on!

HAMMER2 corruption bug and fix

It’s possible to have data corrupted on a HAMMER2 volume during a specific combination of a bulkfree operation and a lot of writing to disk.  Matthew Dillon has a potential fix already.  As he announced, it’s scheduled to go into 5.4 this weekend.  It’s a rare bug, but if you want to check for it, look for CHECK FAIL entries in /var/log/messages.

And because every cloud has a silver lining: some not-yet-quantified performance improvements.