Linux: BtrFS
-
This person definitely got the opposite impression that you did from my comments in that post.
-
Here is the code itself, rather than a third party discussing it:
# These files are writen in a temporary backup dir. Everything is done # in order to minimize donwtime of the guest. For example, it takes # a snapshot of the block devices (if backed with LVM) so the guest is # just paused for a couple of seconds. Once this is done, the guest is # resumed, and the script starts to dump the snapshot.That wording sure makes it sound like LVM is only an optional method, not the sole one.
-
@scottalanmiller said in Linux: BtrFS:
@stacksofplates said in Linux: BtrFS:
@scottalanmiller said in Linux: BtrFS:
@stacksofplates you left out the part where I "recommended" a non-LVM based backup solution for the OP on that old thread and got the BA for it. I use "recommended" loosely as it was just a search for a free tool that would work for him to get what he needed and would not require LVM as he did not have it. That, too, was not a recommendation, it was simply telling him about a tell.
You can't read into every response to a thread as a recommendation or personal endorsement unless it is stated as such. If we did, we'd have to also assume that I had recommended not installing LVM, because he didn't but I still answered, or that I was recommending KVM (which might be great, but I certainly didn't promote it in any way.) There is no end to what we could read in. I simply provided some information, guidance and the accepted BA which did not involve LVM.
If we equally read into my BA response, we'd take away that I had recommended against LVM on that thread. In reality, I didn't recommend any backup style at all, only that LVM not be avoided during installation so that options would be available later.
Ya that's using LVM. Nice try.
Direct quote from the site you linked (the python script I'm talking about)
I use it to backup running virtual machines in this way: first, suspend the virtual machine (for a short while), then create a snapshot of the LVM used as storage by the virtual machine, then resume the virtual machine so it can continue running without almost no downtime (taking a LVM snapshot is very fast!)
It does exactly what you just said you didn't recommend.
Are you sure? I looked in the code and the code made a point of LVM being added later (in the 2011 notes) and sure looked like LVM was only one of the methods supported. It specifically says in the code that some features are only if using LVM. Would be weird if that was the only option.
The part you quoted was someone else talking about how they use the script, they likely had LVM so use it in that way.
The part I posted was the same thing you posted. It was written in 2010. So unless he's a time traveler, that's how it works.
-
@stacksofplates said in Linux: BtrFS:
The part I posted was the same thing you posted. It was written in 2010. So unless he's a time traveler, that's how it works.
But is that the only way that it works? I don't know, I only know that I looked in the code and it said what I posted above.
-
@scottalanmiller said in Linux: BtrFS:
This person definitely got the opposite impression that you did from my comments in that post.
So because someone apparently doesn't understand that Logical Volumes are block storage, that somehow means what you said didn't actually mean what you said?
-
@scottalanmiller said in Linux: BtrFS:
@stacksofplates said in Linux: BtrFS:
The part I posted was the same thing you posted. It was written in 2010. So unless he's a time traveler, that's how it works.
But is that the only way that it works? I don't know, I only know that I looked in the code and it said what I posted above.
See I call bs on that. If you looked at the code then why link some article someone posted about using it as a LVM backup method (and giving instructions on how to do it) instead of the actual product.
-
You are probably right. And looking at the script I'm not seeing if there are multiple methods or not, only looking at it quickly. I'm sure I did a quick search using exactly the words from the title of the thread to get a link to a resource for the OP. I'm sure I didn't look into it at all at the time.
So I apologize for answering his question as he asked it and for being confusing. I meant to imply nothing, just to help him out and answer his question.
-
@scottalanmiller said in Linux: BtrFS:
You are probably right. And looking at the script I'm not seeing if there are multiple methods or not, only looking at it quickly. I'm sure I did a quick search using exactly the words from the title of the thread to get a link to a resource for the OP. I'm sure I didn't look into it at all at the time.
So I apologize for answering his question as he asked it and for being confusing. I meant to imply nothing, just to help him out and answer his question.
I'm not trying to do this to make anyone apologize or feel bad. I just don't understand why on one hand things are recommended and in the same scenario where someone says "imagine I will run KVM server ontop of BTRFS, will it makes sense to snapshot the volume " and you say, "No it's never made sense".
It makes sense and it's a very viable way to do it. Sure it's wasteful, but if you "need" a full image backup, it's a perfectly viable way.
Esp since it's just as fast (or possibly faster) to block copy an image backup onto a volume vs a backup through an agent (like ReaR or Veeam Endpoint).
-
Personally, unless it's absolutely needed, I don't think raw block storage is a good idea. But if you need the block storage, that method is a decent way to do image backups.
-
@stacksofplates said in Linux: BtrFS:
@scottalanmiller said in Linux: BtrFS:
You are probably right. And looking at the script I'm not seeing if there are multiple methods or not, only looking at it quickly. I'm sure I did a quick search using exactly the words from the title of the thread to get a link to a resource for the OP. I'm sure I didn't look into it at all at the time.
So I apologize for answering his question as he asked it and for being confusing. I meant to imply nothing, just to help him out and answer his question.
I'm not trying to do this to make anyone apologize or feel bad. I just don't understand why on one hand things are recommended and in the same scenario where someone says "imagine I will run KVM server ontop of BTRFS, will it makes sense to snapshot the volume " and you say, "No it's never made sense".
Here is what I was trying to say...
- Using LVMs isn't great for your main backups (as a recurring mechanism) because it can't grab the system live without risk because we don't know the state of the storage.
- BtrFS does not change this at all, it has the same limitations that LVM2 did/does.
What I was trying to "imply" (you can see why I'm bad at that) was that other methodologies are available and more effective, such as using a Veeam Agent which will know the state of the storage.
Can snaps be used? Yes, they can. But using them is not straightforward and simple, at best they are part of a bigger backup strategy and not used on their own. You would not "snap the volume" under normal running KVM circumstances. You certainly don't want to disable that functionality just to throw it away, but you would not, or at least I would not, normally snap the KVM storage volume.
You are correct, with the right known limitations and scripting or tooling, the LVM2 or BtrFS snapping mechanisms can play into a larger backup mechanism. Something that can force a quiescence and manage the snap together can make this effective.
-
@stacksofplates said in Linux: BtrFS:
Personally, unless it's absolutely needed, I don't think raw block storage is a good idea. But if you need the block storage, that method is a decent way to do image backups.
I agree, to both parts. The big thing that I was meaning was that I don't generally recommend image backups and then that dominoes into not using snaps for backups (at least not alone). If you need raw storage and images, absolutely, that's how you do it. I wasn't try to say that it wasn't how to do that, but meant not to do that at all (or rarely.)
-
@scottalanmiller said in Linux: BtrFS:
@stacksofplates said in Linux: BtrFS:
Personally, unless it's absolutely needed, I don't think raw block storage is a good idea. But if you need the block storage, that method is a decent way to do image backups.
I agree, to both parts. The big thing that I was meaning was that I don't generally recommend image backups and then that dominoes into not using snaps for backups (at least not alone). If you need raw storage and images, absolutely, that's how you do it. I wasn't try to say that it wasn't how to do that, but meant not to do that at all (or rarely.)
Ya I have done it with just a snap, and things went wrong. Esp when concerning the host. The host has to have the logical volumes mounted (if I remember correctly) so all of that comes in to play also.
-
@stacksofplates said in Linux: BtrFS:
@scottalanmiller said in Linux: BtrFS:
@stacksofplates said in Linux: BtrFS:
Personally, unless it's absolutely needed, I don't think raw block storage is a good idea. But if you need the block storage, that method is a decent way to do image backups.
I agree, to both parts. The big thing that I was meaning was that I don't generally recommend image backups and then that dominoes into not using snaps for backups (at least not alone). If you need raw storage and images, absolutely, that's how you do it. I wasn't try to say that it wasn't how to do that, but meant not to do that at all (or rarely.)
Ya I have done it with just a snap, and things went wrong. Esp when concerning the host. The host has to have the logical volumes mounted (if I remember correctly) so all of that comes in to play also.
Yeah, that just gets unnecessarily complex. It's so rare that a setup like that is warranted.
-
Ya with a preallocated qcow2 I can get pretty close to raw speeds. No one is going to notice 10MB/s or even 20 in normal settings.
-
S scottalanmiller referenced this topic on
