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Unionfs for Linux?
Lukey Boy asks: "A machine in my network is currently a large fileserver, and holds many hard disks full of media (namely my music and what not). Each drive is running a standard EXT3 filesystem with the same layout (/media, /media/mp3, and so on). My problem and question is how do I join these drives to look like a single hierarchy? I would like to, when I check /all/mp3, view the contents of each drive in this combined directory. FreeBSD has a unionfs filesystem type which supports the unioning of two drives - but only two is a fairly bad limitation, especially when I add a new drive. It appears that Al Viro is working on a unionfs for Linux 2.5, with again only two mount points supported. I was also considering using the Linux Volume Manager system, or possibly a software RAID striping arrangement; does anyone have any experiences doing anything similiar? Is there any decent inheritable filesystem (IFS) available for Unix machines?"
I use LVM with reiserfs on all my boxes - resizing both the volume and the filesystem is easy. For instance, if I want to grow my MP3 volume by 10G: "umount /riaa; lvextend -L +10G /dev/quadcuda/riaa; resize_reiserfs /dev/quadcuda/riaa; mount /dev/quadcuda/riaa /riaa". Done. Shrinking is just as easy, but in that case the filesystem resize happens before the volume resize instead of vice versa.
Looks like you could do the same with ext2 and resize2fs if you wanted. If I recall correctly, when I set up my first box with LVM, resize2fs had lots of "beware, this is somewhat experimental code" warnings and I was reluctant to use it, which was one reason why I used reiserfs instead. Maybe a couple more years of testing have increased confidence in the utility, since those warnings aren't there now. I'd rather use reiserfs anyway.