BTRFS as image store for KVM?

2015-09-15 Thread Gert Menke
Hi everybody, first off, I'm not 100% sure if this is the right place to ask, so if it's not, I apologize and I'd appreciate a pointer in the right direction. I want to build a virtualization server to replace my current home server. I'm thinking about a Debian system with libvirt/KVM. The

Re: BTRFS as image store for KVM?

2015-09-17 Thread Gert Menke
Hi, thank you for your answers! So it seems there are several suboptimal alternatives here... MD+LVM is very close to what I want, but md has no way to cope with silent data corruption. So if I'd want to use a guest filesystem that has no checksums either, I'm out of luck. I'm honestly a bit

Re: BTRFS as image store for KVM?

2015-09-17 Thread Gert Menke
On 17.09.2015 at 21:43, Hugo Mills wrote: On Thu, Sep 17, 2015 at 07:56:08PM +0200, Gert Menke wrote: BTRFS looks really nice feature-wise, but is not (yet) optimized for my use-case I guess. Disabling COW would certainly help, but I don't want to lose the data checksums

Re: BTRFS as image store for KVM?

2015-09-17 Thread Gert Menke
On 17.09.2015 at 20:35, Chris Murphy wrote: You can use Btrfs in the guest to get at least notification of SDC. Yes, but I'd rather not depend on all potential guest OSes having btrfs or something similar. Another way is to put a conventional fs image on e.g. GlusterFS with checksumming

Re: BTRFS as image store for KVM?

2015-09-29 Thread Gert Menke
Hi, thank you all for your helpful comments. From what I've read, I forged the following guidelines (for myself; ymmv): - Use btrfs for generic data storage on spinning disks and for everything on ssds. - Use zfs for spinning disks that may be used for cow-unfriendly workloads, like vm

Re: BTRFS as image store for KVM?

2015-09-18 Thread Gert Menke
On 2015-09-18 04:22, Duncan wrote: one way or another, you're going to have to write two things, one a checksum of the other, and if they are in- place-overwrites, while the race can be narrowed, there's always going to be a point at which either one or the other will have been written, while

Switch raid mode without rebalance?

2016-08-25 Thread Gert Menke
Hi, I recently created a new btrfs on two disks - one 6TB, one 2TB - for temporary backup purposes. It apparently defaulted to raid0 for data, and I didn't realize at the time that this would become a problem. Now the 2TB is almost full, and df tells me I only have about 200GB of free space.

Re: Switch raid mode without rebalance?

2016-08-26 Thread Gert Menke
Hi, On 2016-08-26 13:52, Austin S. Hemmelgarn wrote: Regular 'df' isn't to be trusted when dealing with BTRFS, the only reason we report anything there is because many things break horribly if we don't. Yeah, I noticed. Seems to produce a reasonable guess, though. Additionally, while

Re: Switch raid mode without rebalance?

2016-08-26 Thread Gert Menke
Hi Chris, first off, thank you for the detailled explanations! On 2016-08-26 01:04, Chris Murphy wrote: No, it's not a file, directory or subvolume specific command. It applies to a whole volume. You are right, but all I was after in the first place was a way to change the mode for new data

Re: Switch raid mode without rebalance?

2016-08-25 Thread Gert Menke
Hi, On 2016-08-25 20:26, Justin Kilpatrick wrote: I'm not sure why you want to avoid a balance, I didn't check, but I imagined it would slow down my rsync significantly. Once you start this command all the new data should follow the new rules. Ah, now that's interesting. When the balance

Re: Switch raid mode without rebalance?

2016-08-25 Thread Gert Menke
Hi, On 2016-08-25 21:50, Chris Murphy wrote: It's incidental right now. It's not something controllable or intended to have enduring mixed profile block groups. I see. (Kindof) Such a switch doesn't exist, there's no way to define what files, directories, or subvolumes, have what profiles.