On 03/15/2016 02:46 PM, Carlos E. R. wrote:
On 2016-03-15 18:37, jdd wrote:
Le 15/03/2016 18:04, Anton Aylward a écrit :
yes, and it's why I wonder is btrfs subvolumes are better or not. Subvolumes do not need at all fixed partitions, lvm allows easy changing.
as someone said, when fixing problem each level of difficulty is an obstacle. With lvm it's much more difficult to know how the disk is used (let only because the computer owner do not know this himself), devices names are pretty hard to remember, partitioning needs the correct driver version to be read (and chance is you don't have it), etc. If lwm go through several disks, I simply refuse to try.
That's the point.
With LVM you need to learn how to resize the spaces, and spend time doing it. Yes, you do not have fixed partitions, you can add space when you need it. Not always subtract space. But the admin has to do it. Posibly tell LVM to give more space to such "space", then use something to grow the filesystem itself if it is not automatic.
With btrfs subvolumes you do nothing. There are no constraints on the size of any of them, as long as there is free space on the big partition.
That's the whole point: with BtrFS there is *no* partitioning, its all one file system. There are no boundaries. Some people seem to consider this a good thing. While I can see why, I personally don't. I think that being unconstrained leads to poor operational discipline. I think that the "only computer knows" is a ridiculous argument. back when I began my career and there were few compilers and 'structured programming' was a thing of the future I had a manager who insisted we not only coded in assembler so we knew what was going on in the computer, but assembled everything because, as he said about link editors, you didn't really know what what was going on inside the computer. The same applies all the way down: even if you are programming in C or C++ you don't know the code that being produces (and it varies not only by target but also by compiler flags). You don't know where the virtual memory is mapping to physical memory. "Only the computer knows". Yes it will tell you if you ask, but that's for the realm of debugging. Most of us just trust it works and get on with life. The same as we do with all other technology that we don't have to learn the details of. you don't really know about metallurgy and chemistry and more to drive your car. In fact you mechanic probably doesn't either. If you don't think there should be constraints, then why don't you try driving just anywhere on the roadways, ignore signs and traffic lights? Constraints are what make things work well.
Of course it has caveats. If there is corruption, all of them are affected, for instance. LVM also has caveats: it can break, and if it does you need to understand how to boot and rescue LVM.
Yes, anything can break. The problems I've had with LVM I've always traced down to disk hardware and would have afflicted BtrFS as well. The days of simple bad sectors are past, the drive electronics has 'modules' that take care of remapping ... until it all gets overwhelming. There's a lot of "yes it used to be but we changed all that" in late model disk drives. The last time I had a catastrophic disk failure the manufacturer techs gave me a long and detailed explanation of how things now work and why the 'crash' I had was unrecoverable -- no matter what, and regardless of the file system. I've posted before about the use of the rescue disk and chroot to do repairs. it works for LVM as well. I've had file system wipe-outs with BtrFS that were unrecoverable, but no problem with ReiserFS has ever been unrecoverable. LVM also seems to be 'self repairing' in that its internal links and pointers lets the tools recover the structure correctly. *ANY* system needs learning and experimentation. John Andersen said
ts kind of like watching doctors play "hold my beer and watch this" while your kid is in the operating room on the heart-lung machine.
I think that is a spurious argument. Before he got to the operating room the doctor had to go though the years of pre-med education and training, and his education and doctor included a lot of experimentation in educational settings. Even when training in a hospital he was under supervision. its not like the software industry where fresh, inexperienced kids are set loose writing software that might be life-critical or business-critical. I admit that I have the fortunate situation of the junk in the Closet of Anxieties to play with. OK, much of it is way behind in terms of technology, no blazing fast graphics boards, no server boards with 2, 4 CPU slots and room for 128G of memory. Yes, a lot of SPF desktops. But I can still shove a new $50 2T drive on one of those and load up any one of the 32-bit operating systems and kick it around and abuse it. Yes, I'm fortunate.
I don't, I don't want to spend time learning it (not interested), so I made the choice long ago to not use it :-)
I made the decision not to learn about Windows :-0
(nor do I use btrfs)
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