[PLUG] striping in LVM or md?

[Eric Wilhelm]

# from Dan Young
# on Wednesday 06 June 2007 09:13 pm:

>> Anybody got any references to benchmarks on that?  All google gives
>> me is questions.

Ok, so I plugged in a little disk and discovered that indeed I cannot 
create a striped LV from dissimilar sized pv's.  I was hoping lvm would 
give me the performance without the space loss (up until I ran out of 
matched space and then just be a bag of disks after that.)  Nope.

>At work we've got a big LVM VG of md RAID1 pairs. The performance is
>effectively the same as just a single RAID1 array, except where I/O
>happens to different PVs at the same time, in which case, it's, um,
>faster...

Thanks, that's basically what it looks like I'm going to do.  I was 
hoping that I could get "mostly striped", but I guess not.  How linear 
is "linear"?  Does it completely fill the first PV before writing to 
the second?  If so, I guess I could do raid10 in md and tack the 
remaining mirrored 40GB onto the end (but, yeah that's getting 
complicated.)

I suppose I could decide that I only need 100GB or so to be striped and 
then allocate the rest of the VG into one linear bag.

Now if I could just figure out how the heck I ended up with 200GB of 
files...

--Eric
-- 
Anyone who has the power to make you believe absurdities has the power
to make you commit injustices.
--Voltaire
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