lvcreate

[andi_1]

Hi guys,

I am trying to set contigous allocation for my lvm which is striped over two disks:

lvcreate -L 76 -n lvedinfs -s y -C y -i 2 -I 16 /dev/vg01

And I get the following message:
Contiguous allocation for striping isn't
supported.

Man doesn't say that I cannot use Contigous allocation if I use striping... . Is it actually true that I cannot specify Contigous allocation is lv was striped over several disks?

Thank you!

[Thayanidhi · Accepted solution]

You are correct!Man page not showing.
It's not logical to have Contigues
when disk striped.

[Stefan Farrelly]

contiguous and striping are complete opposites so they cant go together. If you have say 4 disks and stripe then block 1 is on disk A, 2 on disk B etc. so how can it possibly be contiguous ? if it was then you would have block 1 and 2 etc. all on disk A - thats contiguous.

[Frederic Sevestre]

Hi,

You can't use contiguous allocation policy and stripping.

Fr??d??ric

[Sanjay_6]

Hi,

Try this from "man lvcreate"

/Quote/

Set the contiguous allocation policy. A contiguous logical volume has three characteristics:

+ Physical extents are allocated in ascending order,
+ No gap is allowed between physical extents within a mirror copy,
+ Physical extents of any mirror copy all reside on a single physical volume.

/EndQuote/

Hope this helps.

Regds

[S.K. Chan]

It's "indirectly" mentioned in the man pages ..
In "-C contigouous" section ..

"physical extents are allocated in ascending order"
"physical extents of any mirror copy all reside on a single Physical volume".

If you got multiple disks the PE "counter" resets to 1 when it hits the the first PE the second disk, so that wouldn't be "..ascending order" already.

[Duncan Edmonstone]

From the man page for lvcreate, an LV with contiguous allocation is defined as:

+ Physical extents are allocated in ascending order,
+ No gap is allowed between physical extents within a mirror copy,

+ Physical extents of any mirror copy all reside on a single physical volume.

So a contiguous LV has to be on a *single* physical volume, ergo it cannot be used with stripes.

The only lvols that *must* be contiguous are root(/), boot(/stand),and swap/dump.

HTH

Duncan