I'm looking to get input on some thoughts I have for configuring laptops with 2008.11.
What I have in mind is changing some of the defaults that you get when you install 2008.11. I'm not advocating any changes to our installers, merely some manual tweaking that might be useful on at least my laptop, possibly others as well. ZFS Since most laptops (if not all) only ship with a single disk, the ZFS root pool we create contains a single vdev. ZFS by default stores multiple copies of metadata but it requires >1 vdev to store multiple copies of data. Unless of course you create your filesystems with the copies parameter (set to 2 or more). It seems to me, that setting copies=2 on our ZFS filesystems on laptops is probably a useful setting to protect (at least as much as we can using a single vdev) from catastrophic data loss due to drive hardware issues. My question is, does copies=2 work the way I'm thinking and more specifically is there a reason we wouldn't want to do this (apart from using more space but I'll get to that in a minute)? Also, does it make sense to set copies >1 on things like the dump and swap volumes? If you set the dump volume to have copies=2 then it takes up twice the space you create (so a 2g dump volume takes up 4g without a dump having been written). A related question to dump volumes is that if we don't have some redundancy via copies=2 do we a) care since dump should just be a copy of memory and only persist until the dump is saved and b) can the system actually run in this fashion. By which I mean if we only have one copy of *data* on the dump volume and the disk gets corrupted in the blocks that the dump volume lives on, what's the failure mode? I don't care really if we just lose whatever dump was there (if there was one) but if the zpool becomes totally unusable because it can't correct the damage then that's a problem. Same sort of questions for swap except I'd imagine we want copies=2 on swap so that we don't just die if swap went away because ZFS couldn't recover from a data failure. On laptop hard disks, it's probably a good idea to enable compression. Partially due to their historically small size but also if we're storing 2 copies of data the compression could help. Disks are getting bigger, but that's neither here nor there for this discussion. I'm sure we don't want to compress the dump device (the exact reason escapes me) but things like rpool/ROOT/opensolaris and rpool/export seem like good candidates. Swap I'm not so sure about. Is there any benefit to compressing a ZFS volume like swap? Anyone know why I can't set the bootfs property on a zpool that has filesystems with compression=gzip and copies=2 set? When I try to set it, it says cannot set property for 'rpool': operation not supported on this type of pool. And the gui installer fails in _get_root_dataset: Could not determine root dataset from vfstab ICT_EXPLICIT_BOOTFS_FAILED. I don't see this failure if I use the default lzjb compression instead of gzip. Which is a shame because lzjb gives you a 1.75x compression ratio whereas gzip (which is really gzip -6) is 2.7x. Is gzip not supported on root pools? Not so much a question, but I'm also thinking that limiting the ZFS arc cache to 1G (at least on systems with <=4G of memory) is a good idea. I've noticed interactivity in Gnome sometimes takes a nose dive if you let the arc consume whatever it wants (regardless of whatever algorithim it uses for freeing things upon demand). So, thoughts? Glenn
