UFS is only supported in read-only mode in a TruCluster setup, while AdvFS is fully cluster-aware and supports full POSIX semantics in a cluster environment (well, except for the times is doesn't :-) ). It doesn't include full LVM functionality (like it can't do RAID except for striping, which is done at the file level instead of the block level), but it does integrate many of the useful parts. You can do snapshots at the filesystem level instead of the block level (which means you don't have to leave disk space unallocated to do snapshots). AdvFS can also have multiple filesets in a single file domain, all sharing space (optionally with quotas on each fileset).
Yup, RAID needed to be done on separate level, but I never missed that one. If you had TruCluster, you'd probably have some external hardware RAID to take care of that. And I really liked the integration of LVM features with file system that advfs had. It simplified things. You want to move bunch of file systems to larger disk. Add it to advfs domain, delete old disk from domain, and voila you are done. No manual file system resizing and stuff.
And yeah, the ability for logical volumes (file sets in advfs speak) to share all the space in volume group (file domain in advfs speak) instead of allocating fixed amount to each volume was really great. We are not going to see this in Linux unless ext3 (or some other fs type) becomes LVM aware.
BTW, Sun DiskSuite (which is basically software RAID implementation, not LVM) can also do snapshots without reserving disk space for it. With DiskSuite, submirror can be either "offlined" or "detached". If you detach/attach submirror, it will be resynced from scratch. However, if you offline submirror, when you online it again, system will sync only changed blocks. So I guess that feautre could be more or less easilly implemented in Linux. Not sure where it keeps what blocks need updating (256 kB of data per 1 GB of disk space). Kernel memory? Swappable memory? RAID metadata stored on disk (such as the space at the end of partition that md uses on Linux)?
Heh, this thread really got wild. From Dovecot vs Cyrus, we got to the kernel wishlist ;-)
AdvFS really rocks; I will miss it (and TruCluster) when the Alpha disappears. Thanks HPAQ! :-(
Yup. Mee too :-(
-- Aleksandar Milivojevic <amilivojevic@xxxxxx> Pollard Banknote Limited Systems Administrator 1499 Buffalo Place Tel: (204) 474-2323 ext 276 Winnipeg, MB R3T 1L7
