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Question about the disk space on mirrored vg00

 
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Waqar Razi
Regular Advisor

Question about the disk space on mirrored vg00

I have a question. Does the free space as given by free extents on a mirrored disk is double the original space? In order to calculate the real space we need to make it half. Is it true?
7 REPLIES
Solution

Re: Question about the disk space on mirrored vg00

In LVM Disks aren't mirrored, logical volumes are mirrored.

So if you have 100 physical extents free in a VG, and you want to mirror whatever LV uses those free extents, you will only be able to create 50 mirrored logical extents (assuming the free PEs are equally distributed across ane even number of disks in the VG.

So simple answer - if you have 100 PEs free in your VG, you can only create a mirrored LV of 50 extents

HTH

Duncan

HTH

Duncan
Ganesan R
Honored Contributor

Re: Question about the disk space on mirrored vg00

Hi,

Answer is NO. Whatever the free extends available is the actual free space.

You should not confuse these free extends with mirror.

Free PE show's by vgdisplay is the total free PE's in that VG.
Free PE show's by pvdisplay is the total free PE's in that PV.

If you are creating non-mirrored lv, you can use the full space. if you are creating mirrored lv, you can use maximum of half of the space.
Best wishes,

Ganesh.
Roopesh Francis_1
Trusted Contributor

Re: Question about the disk space on mirrored vg00

Hi,
If your vgdisplay is showing 100 Free PE,you have 100 PE to create a new non-mirrored Logical volume however you have only 50 free PE to extend/create a mirrored logical volume.
SoorajCleris
Honored Contributor

Re: Question about the disk space on mirrored vg00

Hi Waqar,

Does the free space as given by free extents on a mirrored disk is double the original space?

No - Free space what ever given is correct and you can use that.If it is showing 100 PE free in Vgdisplay you can create a new LV with 100 PE

BUT

If you are extending size of an already existing mirrord LV, It will use double sapce ( for extending 1 PE it will take 1 PE from each disk = 2 PE)

That case if you ask

In order to calculate the real space we need to make it half. Is it true?

YES.

Regards,
Sooraj U
"UNIX is basically a simple operating system, but you have to be a genius to understand the simplicity" - Dennis Ritchie
SoorajCleris
Honored Contributor

Re: Question about the disk space on mirrored vg00

I forgot to mention, it is not the free PE in disk, but in VG.

Still if the mirror policy is wrong and if it is non-strict( by mistake), it will take double space from same disk itself. This is a rare case.

regards,
Sooraj
"UNIX is basically a simple operating system, but you have to be a genius to understand the simplicity" - Dennis Ritchie
Kanagaraj
Regular Advisor

Re: Question about the disk space on mirrored vg00

Hi,

What Ganesan said absolutely right!

Already Mirrored root vg00 has free face(free PE).we can you all free PE to create new LV.

available free PE-100 and PE size-4MB then available free space in VG 400MB.
So we can create 400MB a new LV.

If you want to mirror the new LV then create new LV in root disk and mirror to another disk in same VG.(only use 50PE.

I hope you got the logic.
Jeeshan
Honored Contributor

Re: Question about the disk space on mirrored vg00

Absolutely Waqar, you are right.
a warrior never quits