Questions about growing a meta volume

I would recommend making a new meta with as large a member you can create.  Having a meta with that many members may be supported, but it doesn't mean just because you can do something, that is a reasonable thing to do.

Hi moeen,

we generally increase existing meta in our environment in the following way

1)create a BCV volume of same size as existing meta

2)make new devices which needs to be added.should check the ISCSI persistance settings,if required.

3)then using below command

add dev ***:+++ to meta ###,protect_data=TRUE,bcv_meta_head=///;

But in your case I think you can not get your required target of 16Tb because you already have 164 members in meta.To the

best of my knowledge we can have only 255 members in a meta.so u can add only 91 members of 65GB which give you only

5.7 TB.

He is only going to get 3 TB more space if he choses to add 91 more meta members to exisiting meta. As he had mentioned its striped meta so all new members must be equal to his existing 34 Gb. So the max additional space he is going to get

91 devices X 34 GB = 3094 GB

I agree with Quincy, go for a new meta with bigger meta memebers rather than more meta members..

Also consider that a meta should not wrap (share spindles).

I cannot imagine that this meta isn't wrapping back onto the same disks.

I would never recommend a meta with more than 64 members in practice.

Hi Saurabh,

Thanks for correcting  me..Also it will be helpful if u let me know anything more to be done and precautions to be taken while

expanding existing lun having data.

There is a procedure to expand a striped meta and maintain the stripe it involves the use of a BCV copy of the same size and meta member count as the original meta volume.  Once copied the new meta is created a a force restore is issued to copy the data from the BCV to the new meta size.  Concatenated meta volumes are easier to expand but do not perform as well as a striped meta.  With the size of the meta volume you already have you will need a lot of available space for the striped meta expansion.

If you want to get to a meta with a larger lun size in it then you are looking at having to do a host copy.  You might be able to use powerpath migrator of possibly federated live migration; really not sure there are caveats and you are staying on the same array.

BTW since this is an appliance without a volume manager how will it handle bringing the extra space online to the system?  Some systems are very friendly to expanding a current lun (windows) and others are not at all without a reboot.

Thank you all for your responses. We generally use vxvm to grow volumes on the hosts and not bother with meta expansions, however, this meta is assigned to an appliance that has no volume management capability and it can only use one device. Question still unanswered is do we need to convert stripe meta to concat meta? as I have read that only a concat meta can be expanded. It seems like the only way to get to 16TB is to recreate the meta with bigger memebers as with the current size, we can only get something close to 8 or 9 TB and we can't add members with different sizes. I also read that all meta memebers should be part of the same disk group , Is this true? As for wrapping, all the current meta members are from the same disk group and no other hypers are created on these disks.

Even with all the disks in the same disk group, meta members will be sharing the same disk which is a general no-no.

A single meta volume should not have more than one member on any physical disk.

For example, with RAID5 3+1 (4 disks) the maximum meta member count with 120 disks is 30 members, any more and you will have more than one member on a disk.