Re: For Lenny: LVM, LVM+MD or just MD for mirroring?
On 6 Sep., 00:40, "nate" <debian-u...@aphroland.org> wrote:
> Jens wrote:
> > Just out of curiosity, what exactly did you do?
>
> I'll have to dig up the configs, will send a reply when I find them..
Thanks!
> > OK, I do this with quotas mainly. I haven't yet come across a scenario
> > where these were not sufficient any more. (Except maybe for /tmp and /
> > var which have their own partitions).
>
> Well this is for the file system itself rather than users on the system.
> e.g. allocate 1TB volume to file system thinly provisioned
> format volume
> (size taken on array ~20MB)
> Write 100GB of data to volume
> (size taken on array 100GB)
> delete 100GB of data from volume
> (size taken on array 100GB)
But, unless you need dozens of different file systems which need to
have lots of free space allocated for some reason, which doesn't
really exist, you can achieve the same thing with quotas, right?
> The LVM restrictions is mainly to compensate for the file systems
> inherit inefficiency in not re-using existing blocks that were
> freed before allocating new blocks(sometimes it does but it doesn't
> do a perfect job at it).
??? I don't get it - if I delete a file, the space it used up _is_
freed, right?
> It's a fairly new technology not many storage systems implement it
> yet, though it's a wonderful way to grow on demand. At my
> last company I was able to provision 400% more storage to
> the servers than I actually had capacity. As we got closer to
> the limit of the installed storage system we added more space
> and re-balanced the array for maximum performance, no downtime,
> no impact.
This is what LVM2 does, right? Allowing to grow partitions / volumes
without being restricted to physical volume sizes, by just adding new
space. Saves you having to think years ahead and plan for storage that
isn't going to be used until much later. Or having to add disks later
on and ending up in symlink hell.
> I plan to get an evaluation storage system in next month at
> my company that implements the next generation of thin
> provisioning, which will allow the storage array to
> automatically reclaim space in the file system if it is
> zeroed out. May take a year or two for the software vendors
> to catch up but when they do I'll be ready for even more
> storage efficiency ! I love technology.
What exactly is the difference in "the array reclaiming free space"
and "the file system reclaiming free space" (what it always does)?
I haven't -yet- come across a FS that didn't free exactly the number
of blocks that it previously allocated, when you deleted files. So the
way this looks to me right now is a hugely overcomplicated feature
that already exists in a much simpler way.
But I'm sure I misunderstand something.
Jens
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