Linked by Thom Holwerda on Sun 18th May 2008 15:32 UTC, submitted by sjvn
Sun Solaris, OpenSolaris It seems like we're really on the subject of filesystems and related technology the past few days. We had an interview with the man behind BeServed, an item on WinFS' current status, and now we - possibly - have news on ZFS coming to Linux. Possibly, because it's all speculation from here on out.
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RE[5]: I use ZFS on 1GB RAM
by MattPie on Mon 19th May 2008 20:07 UTC in reply to "RE[4]: I use ZFS on 1GB RAM"
Member since:

hmm....I have to read up on LVM again. I was sure that the lvmove command basically moved all files from a specific pv and moved the data to the space available in the vg. If thats not the case, then yeah, I guess you were kinda screwed. :/

You're correct. I suspect the original poster made a VG with 3 disks, and an LV that took up all the space in that VG. In that situation, you'd have to:
- Use 'resize2fs' (assuming ext2/3) to shrink the file system to fit on the two remaining disks.
- Use 'lvreduce' to shrink the LV to fit on the remaining disks. Make sure the file system is smaller than the LV!
- Use 'pvmove' to move the extents off the PV to be removed.
- Use 'vgreduce' to remove the PV from the VG.

The lesson here is to only allocate space to a volume when you need it. Don't just make a giant LV that takes up all your space. It's a lot easier to expand a volume than it is to shrink it. You can even expand a ext3 file system while it's on-line.

Also, ZFS is fantastic. I have a few Sun T-series boxes and it's just so damn easy to use.

Reply Parent Score: 2

RE[6]: I use ZFS on 1GB RAM
by phoenix on Wed 21st May 2008 05:01 in reply to "RE[5]: I use ZFS on 1GB RAM"
phoenix Member since:

The lesson here is to only allocate space to a volume when you need it.

That's the one thing I can't stand about the current state of volume management on Linux: you have to allocate your disk space at logical volume creation time!

What's the point of having 5 TB of disk space available if you have to determine how to partition it before you start using it?

I used to be a big proponent of LVM, and have used it a lot on multi-disk arrays (mainly for storage of Xen and KVM virtual machines), and it does have it's uses. But having to figure out exactly how much space will be used by what when creating the LV is a pain. And if you get it wrong, re-doing it is even more of a pain.

Add to that the whole "save space for snapshots" issue, and LVM is starting to become more of a pain than plain partitioning.

After using ZFS for the past couple of weeks, creating raidz pools, creating filesystems for /usr, /usr/local, /var, /usr/ports, /usr/src, /usr/obj, /home, /home/user1, /home/user2, basically creating a filesystem when needed, and then setting the properties on a per-filesystem basis (gotta love inheritance) without having to worry about getting the space allocations perfect at the get-go has been a godsend. Just set quotas as needed (when needed) and let zfs manage the rest.

Add to that snapshots you don't have to save space for, and that take next to no time to create, and very little time to rollback, and you have a storage management system that makes DM+MD+LVM look archaic.

Reply Parent Score: 2