LVM2 features
So, what features of LVM actually work in LVM2 if you have version 2.00.15 of the tools, and version 2.6.8 of the kernel?
Do snapshots work?
Does pvmove work?
Are there interesting and weird limitations people should be aware of? Are there things that are distinctly better about those features than their LVM1 equivalents?
Thanks,
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"It does me no injury for my neighbor to say there are twenty gods or no God. It neither picks my pocket nor breaks my leg." --- Thomas Jefferson "Go to Heaven for the climate, Hell for the company." -- Mark Twain -- Eric Hopper ([email protected] http://www.omnifarious.org/~hopper) --
Eric Hopper posted the query below last weekend, but I've seen no replies on the list.
I'm a happy Linux 2.4.x kernel user with LVM 1 for a couple of years now, with no problems and great reliability, on around 30 machines running various Slackware versions.
Eric's question is exactly what I'd like to know, before migrating these production machines to the 2.6.x kernel.
Should I wait? Should I worry? Do I have to buy a Redhat Enterprise to be sure I have magic patches from Redhat in the kernel for reliable LVM2 operation?
I'd really like to hear from the users and developers on this list before changing systems that have been working fine.
Thanks to all,
John
Quoted 13 lines · Eric Hopper
So, what features of LVM actually work in LVM2 if you have version 2.00.15 of the tools, and version 2.6.8 of the kernel?
Do snapshots work?
Does pvmove work?Are there interesting and weird limitations people should be aware of? Are there things that are distinctly better about those features than their LVM1 equivalents?
Thanks,
-- Eric Hopper ([email protected] http://www.omnifarious.org/~hopper) --
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__________________________________________________________________ John Seifarth http://www.waw.be/waw/ Words & Wires SPRL [email protected] Computer Consulting & Language Services Voice: (+) 32-2-660-3943 1160 Brussels, Belgium Fax: (+) 32-2-675-3922
Quoted 2 lines · John Seifarth
Eric Hopper posted the query below last weekend, but I've seen no replies on the list.
Here are the things I've seen...
Snapshots of the root partition seem dodgey. Someone claims that they work on the latest LVM2 client library.
Snapshots of other partitions seem to work OK.
pvmove has lots of weird and arcane limitations that make no sense to me at all. It acted very strangely and seemed to lock parts of my system when I tried it with a fresh Fedora Core 2 install, and I've been afraid to try it since. I see lots of messages flying back and forth about people having to hand-construct command lines to move specific extents because of some odd limitation of pvmove.
I also see little hard information about these limitations or why they exist. I see all kinds of confused posts stating that this detail or that detail is the reason some particular operation doesn't work quite right.
I used to know some of the LVM developers personally, and this list used to be much more open about the internal workings of LVM and there used to be people who would state plainly and authoritatively what was causing some particular problem. I remember fondly the debates over getting /boot onto an LVM partition.
I don't know what's happened or why.
From the outside, it seems as if LVM2 (which by all accounts is much higher quality code) was rushed into production before it was feature-comparable to LVM1, and all the developers are embarassed about it and not talking frankly about what's wrong. If this were not Open Source, I'd say the company they worked for was discouraging them from discussing the limitations openly and leaving the users to guess and talk amongst themselves about them.
Maybe I'm wrong.
*sigh*,
Signature · 4 lines
"It does me no injury for my neighbor to say there are twenty gods or no God. It neither picks my pocket nor breaks my leg." --- Thomas Jefferson "Go to Heaven for the climate, Hell for the company." -- Mark Twain -- Eric Hopper ([email protected] http://www.omnifarious.org/~hopper) --
Quoted 6 lines · Eric Hopper
Quoted 2 lines · John Seifarth
Eric Hopper posted the query below last weekend, but I've seen no replies on the list.
Here are the things I've seen...
<snip>
Quoted 7 lines
pvmove has lots of weird and arcane limitations that make no sense to me at all. It acted very strangely and seemed to lock parts of my system when I tried it with a fresh Fedora Core 2 install, and I've been afraid to try it since. I see lots of messages flying back and forth about people having to hand-construct command lines to move specific extents because of some odd limitation of pvmove.
Quoted 5 lines
I also see little hard information about these limitations or why they exist. I see all kinds of confused posts stating that this detail or that detail is the reason some particular operation doesn't work quite right.
As a user on the outside who loved LVM1, and has grown to love LVM2, I have to say I disagree with your points. This one, for instance, isn't true. The hard data is that the allocation routines in pvmove don't yet understand how to split the destination among two non-contiguous blocks of physical extents. So, even if vgdisplay shows 100GB free, and you only want to move 30GB .. you *might* have to move it in pieces, if the free space isn't in a contiguous block.
Is that as nice as pvmove in lvm1? No. Are the other positives in LVM2 worth dealing with this minor inconvenience? IMHO, Yes!
Quoted 6 lines
I used to know some of the LVM developers personally, and this list used to be much more open about the internal workings of LVM and there used to be people who would state plainly and authoritatively what was causing some particular problem. I remember fondly the debates over getting /boot onto an LVM partition.
I haven't seen any dodging. What I've seen is a tad less active participation in the mailing list by the developers. This makes sense to me.. they're busy making LVM2 better.
Quoted 10 lines
I don't know what's happened or why.
From the outside, it seems as if LVM2 (which by all accounts is much higher quality code) was rushed into production before it was feature-comparable to LVM1, and all the developers are embarassed about it and not talking frankly about what's wrong. If this were not Open Source, I'd say the company they worked for was discouraging them from discussing the limitations openly and leaving the users to guess and talk amongst themselves about them.
This attitude confuses me. Open Source code doesn't really get "rushed to production". If it sucks, people don't use it. There are no big emotional attachments to it like with commercial software, where huge amounts of licensing costs get spent on bad software. I haven't seen anything "wrong." Bugs happen, and they're being fixed fairly quickly.
Maybe its just that this list has reduced in importance wrt LVM2?
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Clint Byrum <[email protected]>
Quoted 7 lines · Clint Byrum
As a user on the outside who loved LVM1, and has grown to love LVM2, I have to say I disagree with your points. This one, for instance, isn't true. The hard data is that the allocation routines in pvmove don't yet understand how to split the destination among two non-contiguous blocks of physical extents. So, even if vgdisplay shows 100GB free, and you only want to move 30GB .. you *might* have to move it in pieces, if the free space isn't in a contiguous block.
That implies another weird problem, which is that you can't pvmove something in a single chunk unless you have the much free space, which is also somewhat non-intuitive.
Quoted 2 lines
Is that as nice as pvmove in lvm1? No. Are the other positives in LVM2 worth dealing with this minor inconvenience? IMHO, Yes!
What are those positives? I don't deny that they exist. I know, for example, the the whole idea of having device mapper for doing the raw block mapping, and actually doing most of the work of keeping track of LVM objects and structures in userland is an excellent idea, and is a much cleaner split than the LVM1 userland/kernel split.
Quoted 3 lines
I haven't seen any dodging. What I've seen is a tad less active participation in the mailing list by the developers. This makes sense to me.. they're busy making LVM2 better.
Maybe the user community is changing, so the quality of the questions and the percentage of high quality answers is going down. Since it isn't so much of a cutting edge thing anymore, the scaling from developer to user is no longer quite so smooth. That observation is not meant as a negative reflection of the user community. This happens to every piece of software as it enters widespread use. Not everybody can be experts in everything.
Quoted 2 lines
This attitude confuses me. Open Source code doesn't really get "rushed to production".
Actually, it does. The Linux kernel development model has tended to cause things to get pushed into 'production' (i.e. major .even kernel releases). Perhaps if kernel release cycles were shorter, this effect wouldn't be so pronounced.
Quoted 4 lines
If it sucks, people don't use it. There are no big emotional attachments to it like with commercial software, where huge amounts of licensing costs get spent on bad software. I haven't seen anything "wrong." Bugs happen, and they're being fixed fairly quickly.
Well, the developers themselves usually have a pretty strong attachment to the idea of widespread usage of their software. I know that's my biggest reward as a developer.
Quoted 1 line
Maybe its just that this list has reduced in importance wrt LVM2?
I'm guessing that's the case because of the user community changes I mentioned earlier.
Have fun (if at all possible),
Signature · 4 lines
"It does me no injury for my neighbor to say there are twenty gods or no God. It neither picks my pocket nor breaks my leg." --- Thomas Jefferson "Go to Heaven for the climate, Hell for the company." -- Mark Twain -- Eric Hopper ([email protected] http://www.omnifarious.org/~hopper) --
Quoted 2 lines · Eric Hopper
So, what features of LVM actually work in LVM2 if you have version 2.00.15 of the tools, and version 2.6.8 of the kernel?
Strongly recommend updating to a recent version of the tools:
Various bugs have been fixed since April!
Alasdair
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