EVA4400 - Continuous access and replication with every virtual disk

[Agustin.J]

Hi,

We are going to install 2 x EVA4400 (named EVA1 and EVA2). We have 2 groups of data (VDISK1 and VDISK2) and would like to do the following:

- EVA1 will be the active storage device for VDISK1 and standby device for VDISK2.
- EVA2 will be active for VDISK2 and standby device for VDISK1.

We want to balance the working load of every EVA, that´s why we want to distribute the VDISKs that way. I guess we need continuous access LTU so that in case one EVA fails we have instant access to current updated information of VDISK1 or VDISK2.

Is all that possible?

Thank you.

[Uwe Zessin]

It depends on your expectations. The failover is not "instant", because the 'standby vdisk' appears on new SCSI targets. Depending on the OS it could be as bad as a reboot of the server(s).

[Agustin.J]

Thanks Uwe.

Let´s leave the "instant" issue aside, about the solution: Can I allocate a different active storage device to every VDISK as explained above?

Thanks.

[Uwe Zessin]

Not sure what you mean by "active storage device", so let me try to explain it in a different way.

The EVA replication works on virtual disks. A 'source virtual disk' that is read / written to by the servers and a 'destination virtual disk' located on a second EVA, that is usually not even visible to any server.
It is important to understand that an EVA virtual disk is not the same as an MSA200/P2000 'virtual disk'

MSA/P2000: virtual disk ~= EVA disk group

MSA/P2000: volume ~= EVA virtual disk
== is presented to one or more servers

And CA source and destination virtual disks can exist in the same disk group and managed by the same or different controllers at the same time.

On the MSA2000/P2000, a virtual disk and all contained volumes are managed by one controller at a time. An EVA disk group is not exclusively owned by a controller.

[Agustin.J]

Uwe,

I am not familiarized with SAN terms, once I have read your explanation, let me please reformulate the question:

We are going to install 2 x EVA4400 (named EVA1 and EVA2). We have 2 VDISKs (VDISK1 and VDISK2) and would like to do the following:

- Some servers will read/write from/to source virtual disk VDISK1 from EVA1, unless this EVA1 fails, in that case EVA2 would be the Storage Device where those servers can access to, with updated information.

- Other servers will have their source virtual disk VDISK2 from EVA2, accessing directly to EVA1 only if EVA2 fails.

So we have 2 VDISK, in every EVA one of them is source and the other one destination, for the servers associated.

Have I explained myself better now?

Thanks.

[Uwe Zessin · Accepted solution]

Yes, that is possible. It is even possible to replicate multiple virtual disks (e.g. VDISK3,VDISK5,VDISK7) from EVA1 to EVA2 _and_ another set of virtual disks (VDISK4,VDISK6,VDISK8) from EVA2 to EVA1.

[Agustin.J]

Thank you Uwe. I see it clearly now.

[Agustin.J]

I got the information I was expecting. I can close this thread.

[Mohammed Iqbal_1]

Hi Uwe,

There is another option that you may consider depending upon the operating system you are running on your servers. For example if you are using HPUX then you could use MirrorDisk optional software to mirror LUNS from each EVA and set primary paths alternatively. This means if you lost one EVA your servers will continue working as normal. However if your server operating system does not support a software based mirroring then this option is no good to you.

If I could afford 2 EVAs I would put them in different physical locations say ~10km apart for site redundancy.