EVA SnapcloneTheory - Mirror-and-break or One-shot?

[Ian Dennison_1]

Having come from an EMC background, having trouble understanding the EVA Business Copy concepts. Have read the manuals / course notes and are none the wiser.

Snapclone creates an entire full size vdisk copy, that we can use to duplicate a database. However, there is only 1 command - the "ADD COPY" command.

Question: Does this start the replication and wait until this replication is complete? Doesn't this take a while? I am looking at a 500GB Database, is it going to be quicker to use Tapes?

Share and Enjoy, Ian Dennison

[Uwe Zessin · Accepted solution]

By default, I think it does not wait, but if I remember correctly, there is a WAIT qualifier for the "SET OPTIONS" command.

You could install the Replication Solutions Manager (RSM) which provides a script environment which gives you more control.

Starting with XCS V6 (so, you need an EVA 4000/6000/8000), you could also use a "mirror-clone". Imagine that the EVA keeps two virtual disks synchronized. You can break the mirror and immediately have a current copy of your data.

[Ian Dennison_1]

Thanks Uwe.

I imagine I will want the script to wait as the database being duplicated will be shutdown while the "add copy" takes place. We were planning on using SSSU to control this.

We have an EVA-5000 with no plans for the 4/6/8000 in the immediate future.

Share and Enjoy! Ian

[SAKET_5]

Ian,

The command you want is:

ADD COPY VDISK= WAIT_FOR_COMPLETION

Info on WAIT_FOR_COMPLETION switch from the SSSU doc:
Waits until the commandâ s operation completes before displaying the next SSSU
prompt (and returning control) or before running another script line. For large
(greater than 1 TB) virtual disks, using this option can result in a long period
before the prompt displays.

[SAKET_5]

By default, as Uwe mentioned, the command is run by the NOWAIT_FOR_COMPLETION switch.

Info on NOWAIT_FOR_COMPLETION switch:
Default. Returns control as soon as possible. Some operations are invalid until the
initial operation completes in the background.

[Bill Costigan]

I do not believe the WAIT_FOR_COMPLETION really waits for the whole 500GBs to be duplicated. It only waits for the initial setup to complete.

However, once that is complete you can start using the copy. The EVA keeps track of the blocks that have been duplicated and those that haven't. It will also immediately duplicate any block that is changed on the primary or copy.

So except for the higher I/O rates in the background there is no reason to wait until the complete 500GBs are copied.

[Sheriff Andy]

Ian,

What VCS version are you running? You might be able to use containers instead. Here is a sample of one our EVA snap clone SSSU Scripts;

# sssu "FILE sssu_script"


SET OPTIONS NOCOMMAND_DELAY ON_ERROR=EXIT_ON_ERROR
select manager sma.somewhere.com username=xxxx password=xxxx
select cell EVA01
add COPY SCdisk1 VDISK="\Virtual Disks\Hosta\Disk1\ACTIVE" DISK_GROUP="\Disk Groups\Slow_250GB_Disks" REDUNDANCY="Vraid5"WORLD_WIDE_LUN_NAME=6005-08B4-0010-3E67-0000-4000-026D-0000
add lun 72 VDISK="\Virtual Disks\Hosta\SCdisk1\ACTIVE" HOST="\Hosts\HP-UX\Hosta"
exit

[Ian Dennison_1]

All,

Had a meeting with a 3rd party support company, who managed to explain it. Turns out that the EVA uses "snapshot" technology (tracking changed blocks) to make the clone copy (complete copy) available almost straight away, then migrates the relevant disk sectors to make a consistent full copy in background. This means it will service any request from the live disk copy for update, plus any request for read/write for the cloned disk copy.

Bill, you were right after all, sorry about the smaller points ration.

Share and Enjoy! Ian

[Uwe Zessin]

Well, that's why it is called SNAPclone ;-)

[Alzhy]

Ian, here's a simpler view:

EVAs (at least on our VCS 3.028 EVA5Ks) do "SnapShots" and "SnapClones". What's the difference?

SnapShots -- is however you and I understand it. Exactly the same as any other SnapShot technologies hardware or software...

SnapClones -- these start off as SnapShots (hence the immediate usability of the "Clones") but eventually result in stand-alone vdisk copies of the original.

Note: Whilst the SnapClone is not fully done, expect some performance hits on the connected servers to the EVA. So plan carefully as the EVA5K is not really that scaleable under some scenarios...


Hope this helps..