BCV verses Clone

It's true we can say that when we activate a clone session we DO have a point in time copy of the SRC data (consistency is something a little differend and usually involves more then a single device) ..
This PIT copy (the TGT device) is a merge between tracks already copied (that are already in the TGT device) and tracks still waiting to be copied (tracks that are still pointers from the TGT device to the SRC device).

I know it's somehow impossible .. But just imagine that right after having activated your beloved clone something (like a pair of muon or a very heavy neutron ) strikes your SRC device .. And your SRC device becomes something like a fried potato. Your clone will have some tracks already copied while some other are still pointers to the SRC device .. But now you don't have a SRC device. Where will the pointers point ?? Do you think you still have a PIT copy ??

With TF mirror when you do issue a symmir SPLIT, you get a FULL and INDEPENDENT copy of your production data, whatever may happen after the split.

This does not mean that TF Mirror is better then TF Clones .. It means only it's DIFFERENT and I simply want to stress what's different. There are a lot of other things that are different .. but right now we are talking about what you have after a SPLIT and after an ACTIVATE ..

In both cases you have a PIT copy .. with TF Mirror the PIT will be a full and independent copy while with TF Clone you'll need to wait untill the TGT becomes Copied to have a full and independent copy.

From this point of view TF Clone looks a lot like TF Snap ... the VDEV will "mean something" only as long as the SRC devices will be available. No SRC device, no VDEV. No SRC, no party ..

Dynamox you are right when you say that every change made at the tracks by the hosts will be captured and handled by the DMX .. That's why I talked about fried potatoes

I can think at 2 things that may suggest to avoid clones:

1) the background copy after the activation may impact the production
2) the failure of "something" (i.e. a pair of disks) may destroy your SRC devices

In both cases you need a FULL and INDEPENDENT copy of your SRC devices.
Both TF clone and TF mirror gives you a full and independent PIT copy of your SRC devices.

But while with TF mirror you have both the PIT and an independent copy when you issue the split, with TF clone you have only the PIT when you do activate and you have to wait (an unknown time) to have your independent copy.

The question is: DOES IT MATTER ?? .. In most cases the answer is NO .. So if it does not matter, you CAN choose between clones and mirror .. And usually you'll choose CLONES. In some cases the answer is YES .. and if the difference matters, you simply CAN'T choose

i am going to throw another variable at you. i am using raid-5 bcvs so obviously they are running in clone emulation mode. When i issue my symmir establish commands , its doing symclone -precopy in the background...then when hey are synced i am going to issue my symmir split. so in the background its really issueing an activate. So taking that its safe to say that when you do a split on raid-5 bcv ..you do not have an independent copy right away.

AFAIK raid5 bcvs are clones .. so you have to treat them like clones. The "real" TF Mirror uses unprotected or mirrored BCVs and moves one (or both) the mirror copies from the BCV device to the M3 and/or M4 column of the STD device, using the "mirroring" that the box offers from ages to obtain the full independent copy that TF Mirror gives

If you think at the meta expansion using BCV to protect data, you'll remember that you can only use unprotected or 2-way-mir bcv .. and guess what is the reason

BTW Dynamox .. are you from Kiev

snooping around Vmware forums ?

i am just curious where did you get that i was from Kiev.

Doing some work on Celerra this morning (enabling Unicode and starting CIFS), so yeah ..you can say "very exciting" day

I don't like football but I know that there is a team named Dynamo Kiev .. That's all ...

I was showing my wife how to use a powerful (and free) photo editing software .. And from time to time I give a look at the forums .. In case someone is having troubles with clones in the weekend :-P

-s-

Hmmm I'm not really into vmware .. But should I jump also in the VmWare forums ?? Is there something that worth having a look at ?? Would you suggest me where to have a look at ??

-s-

PS it seems that both of us have a very boring weekend

I will spend my 100th post to wave you a good saturday with Celerra !! See you next week .. I have scheduled some tests with the same devices in multiple DGs and the symapisrv ...

Bye, have a good time .. and give a hug to your celerra !!

yeah, Dynamo used to be my team when i lived there . You don't like football? I would be careful saying things like that on this forum, your Italian co-workers will have you deported from the country

Stefano...I know this post is 3 years old, but can you tell me the reason why?

thanks....