Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On 15/05/17 02:11, Michael Hierweck wrote: > Hi all, > > up to now to use LVM (thick) provisioning to provide virtual disks for > VMs: RAID => LVM => LV => DRBD => KVM/QEMU (virtio). > > We would like to be able to take snapshots from our virtual disks in > order to be able to use them as readonly source to consistent backups. > Therefore we would need to introduce a LVM thin provisioning layer > somewhere. > > A. TP below DRBD > RAID => LVM => LVM-TP => LV => DRBD => KVM/QEMU (virtio) > > - simple setup > - I suppose going back to an older snapshost would this break DRBD and > require a complete resync/verify run This is what I do. When I need to restore a snapshot, I have done the following: dd from the snapshot to a temp file elsewhere (or increase the snapshot size to be larger than the original disk image) dd from the temp file to the DRBD device, we expect to get a write error/run out of space at the end, because we can't write the DRBD portion at the end of the drive. I haven't attempted it, and it would be interesting to hear the required process to simply use LVM to rollback to the snapshot, but suspect the following steps are needed: 1) Stop the DRBD device (both primary and secondary) 2) rollback the LV using LVM tools 3) Start the DRBD device on the primary only 4) Re-initialise the DRBD device on the secondary 5) Start the DRBD device on the secondary Comments? Personally, that method doesn't work for me, since I can't "stop" the DRBD device because it is constantly open (exported via iscsi) > B. TP on top of DRBD > RAID => LVM => LV => DRBD => LVM => LVM-TP => LV => KVM/QEMU (virtio) > - complex setup > - more layers affect reliability and performance > - snapshots are replicated and consistent > - additional diskspace for snaphosts is limited by the DRBD volume size > an connot be shared across volumes. > > > I would like to discuss the pros and the cons of both approaches while > considering internal vs. external metadata. -- Adam Goryachev Website Managers www.websitemanagers.com.au