Hammer Basics

shakeshuck

I have recently been introduced to UNRAID, and find some of its ideas interesting. This caused me to wonder what Hammer had to offer, and if some of UNRAID's ideas could be reproduced in DragonFly. The Hammer docs are imposing to say the least, but after having skimmed over a few, it brought some questions to mind:

1/ If I create a multi-volume filesystem, is it possible (after the death of hardware, for instance) to mount a single volume from the group on another machine and retrieve the contents, or does the whole filesystem need to be mounted together? Is there a utility to find filesystems spanning multiple volumes?

2/ In case of a disk failure in a multi-volume filesystem, what is the procedure for recovery? I'm guessing any PFS would not be restricted to a disk, but would potentially span multiples, so you would have to have a 'top-level' PFS mirror covering the whole filesystem? Or have I missed something obvious?

Thanks.

daftaupe

Hello shakeshuck,

first of all, HAMMER, from what I understood is considered sort of a dead-end, thus the developpement of HAMMER2.

1/ Never tried, but I guess that from this line from hammer(8) you can't :

Remember that you have to specify device, together with any other device that make up the file system, colon-separated to /etc/fstab and mount_hammer(8).

You can list the volumes being part of a filesystem with hammer volume-list <filesystem> it seems (again from that man page only).

2/ I guess the procedure might be to upgrade a slave PFS to master if you have one. You can check the section " RESTORING A PFS FROM A MIRROR" in hammer(8). Otherwise restore from a backup, I'd say.

I think your questions would be best answered by M. DILLON on IRC/mailing list.

shakeshuck

Hi daftaupe
Good logic with the mount command - I should have thought of that.

I was thinking of using DFly/Hammer AS a backup; not wanting to backup the backup (!) unless simple mirroring is in place.

I did contemplate the mailing lists, but the hammer archives looked as quiet as things over here!

Thanks for the input.