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Create Striped lv on VG having different size disks?

 
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Valued Contributor

Create Striped lv on VG having different size disks?

Hi,

I am having a vg containg 6 disks. Five 100GB disks and One 200GB disks.

Is it possible for me to create an striped lv on this vg using all PE ?

Thanks and Regards,
Manoj K
27 REPLIES 27
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Acclaimed Contributor

Re: Create Striped lv on VG having different size disks?

Please think about - fisrt PE on the first disk, second PE on the second disk ... etc; until the first 5 disks are full. Then you cannot stripe anymore.

Hope this helps!
Regards
Torsten.

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Valued Contributor

Re: Create Striped lv on VG having different size disks?

`
I think what he's saying is that yes you can build striped LVs across this but eventually you will have 600GB of striped LVs and 100GB of free space on your 200GB disk.

-klb
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Trusted Contributor

Re: Create Striped lv on VG having different size disks?

If I'm remembering correctly the LVM selects free extents round-robin from any device with free extents, so the first 600GB will be LVM-striped and the last 100GB worth of the volume will be on the last 100GB of the sixth disk, not striped at all.
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Valued Contributor

Re: Create Striped lv on VG having different size disks?

Hi,

While running a lvcreate am getting the following error.

#lvcreate -l 5594 -i 6 -I 128 -n lvol1 vg03
Warning: rounding up logical volume size to extent boundary at size "716544" MB for striping.
Logical volume "/dev/vg03/lvol1" has been successfully created with
character device "/dev/vg03/rlvol1".
lvcreate: Not enough free physical extents available.
Logical volume "/dev/vg03/lvol1" could not be extended.
Run the "lvextend" command to create space on the Logical Volume.

Please assist whether there is anything extra needed in the command.

Manoj K
Thanks and Regards,
Manoj K
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Acclaimed Contributor

Re: Create Striped lv on VG having different size disks?

Hard to tell without having a

# vgdisplay -v /dev/vg03

But if one of the disks is already full (no free PEs left), you cannot do this striping anymore.

Hope this helps!
Regards
Torsten.

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Honored Contributor

Re: Create Striped lv on VG having different size disks?

RE: "...Is it possible for me to create an striped lv on this vg using all PE ?..."

First Problem:
Depends upon what the volume group's first disk was during creatation. If the first disk was the 200GB disk then n/p. If the 100GB disk then this is what the vg sets it boundaries too. The only way to change this is to destroy the vg and create a new vg stating that the 200 GB disk in the first position.

Second Problem:
Stripping writes PV1 PV2 / PV2 PV1. So eventually you'll hit the 100GB ceiling and be left with 100GB unused on the 200GB PV. And LVM will stop at this point since there is no way for LVM to revert back to writing contiguous.

Comment: I don't know who is advising you to use this obsolete procedure, AKA Software Raid Zero. But there is absolutely no advantage to it in any way, especially in administration or fault tolerance. For you to have fault tolerance you'd have to create a pvgroup of the disks and then mirror the group to another group of the same number of disks, hence raid 01.

Most disk arrays do this for with much less effort and much better performance.

Do not expect better performance. In many years of hearing others report on this configuration no has ever reported better performance. Why? Added O/S overhead.
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Honored Contributor

Re: Create Striped lv on VG having different size disks?

Don't forget to assign points to all of the responses
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Valued Contributor

Re: Create Striped lv on VG having different size disks?

Hi Michael,

<< Comment: I don't know who is advising you to use this obsolete procedure, AKA Software Raid Zero

How can you say that raid0 is an obsolete procedure.I have vraid 1 in EVA and that luns are presented to my server. So again i need to do mirroring (raid1) in OS level?

<
So you are saying that there is no performance adavance in raid0 compared to raid1.

This is the first time i am hearing raid0 obsolete and there is no advantage for raid0 over raid1.

Anyway i am planning to unpresent the 200GB disk and split it in to 2 *100GB disk in eva. Present both disks to the host and create lv with stripe (raid0).

Manoj K

Thanks and Regards,
Manoj K
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Acclaimed Contributor

Re: Create Striped lv on VG having different size disks?

IMHO what Michael say is - it makes probably no sense to stripe across EVA LUNS, because the EVA already does it (maybe better than the OS can do).

Hope this helps!
Regards
Torsten.

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those who understand binary, and those who don't.

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