Questions about Business Copy EVA & backups

[Russ_44]

Hi, I have a couple questions about Business Copy EVA, which we've just purchased and not yet installed.

The software includes a server CD, to load the software and license on the Management Appliance. I understand that.

But it also includes "host agent" software, which (I would assume) has to be loaded on the servers which connect to the EVA. My question is:

What is the host agent software used for? Can't I present snapshots/snapclones to hosts that aren't running the host agent software? What benefits/features do I gain by loading the host agent software on my Solaris and Windows 2000/2003 servers?

Second question:

I was told business copy snapshots would allow me to do point in time backups of my data. I understand how that works -- take a snapshot, present it to a backup server, and run the backup. No problem there.

However, when that backup runs, the backup software should set the archive bit on the files being backed up so that I can run incremental backups later, rather than full backups every time. How will that work? If the backup software sets the archive bit on a file in a snapshot, is it also set on the original data? i.e., are changes to the snapshot written to the original?

Apologies if these are naive questions.

Russ

[Peter Mattei]

Hi Russ

1. Out of the EVA BC Manual:

Host Agents
The BC host agent software is installed on a host computer. This software:
- Provides communication between the host computer and the BC server.
- Performs all activities associated with running BC jobs within the BC network, as directed by the BC server.
- Provides a command line interface (EVMCL) for creating and running BC jobs.

2. You BC volume is a logical copy of the primary volume, you just copy a blockmap. So, you have two independent representations of volumes. As long as neither is changed both reference the very same physical blocks.
If you change anything, like data or the archive bit, the corresponding block is copied to the pool area and thus the primary and the secondary volume point somwhere else. This is called copy on write!

That easy
Cheers Peter

[Russ_44]

Peter,

Thanks for your quick reply. However, there are still a couple things I'm not clear on.

> This software (BC host agent):
> - Provides communication between the host computer and the BC server.

But is the BC host agent software required for snapshots to work? I can create a snapshot and present it to any host I want, can't I? Must the host agent software be loaded on any host I want to present a snapshot to?

> - Performs all activities associated with running BC jobs within the BC network, as directed by the BC server.

I know I'm displaying my ignorance here, but I just don't understand what the point is. BC is used to make snapshots and clones. What is a "BC job?"

As for the second question, about the archive bit and backups. Maybe I should be more clear about the scenario I'm envisioning:

Windows 2003 cluster provides file server front-end to public network, with large EVA/SAN volumes storing the data. I have a dedicated Windows 2000/Netbackup 4.5 server for backups, to be written to the SAN-attached tape library.

Step 1: Make snapshot of fileserver volume.
Step 2: Present snapshot to backup server.
Step 3: Make full backup of snapshot.
Step 4: Unpresent snapshot from backup server.
Step 5: Eliminate snapshot.

Next night:

Step 1: Make snapshot of fileserver volume as it exists now, one day later.
Step 2: Present snapshot to backup server.
Step 3: Make incremental backup of snapshot. Only those files changed since the last backup should be backed up today.
Step 4: Unpresent snapshot from backup server.
Step 5: Eliminate snapshot.

Simply put, I don't know that this will work.

More apologies for being dense...

Russ

[Uwe Zessin · Accepted solution]

Russ,

BC-EVA is really two things:
1) the 'snapshot' license for the EVA which is entered on the Storage Management Appliance (SMA)
2) a 'management framework' that runs on the SMA - it was formerly called Enterprise Volume Manager (EVM) and a separate product. It consists of the BC GUI and the BC server running on the SMA and the BC host agents running on the hosts.


The host agent is not required to initiate a snapshot and present it to a host. You can also do that through the 'Storage System Scripting Utility' (SSSU) that is included in each operating system's platform kit. The SSSU is a command-line interface that talks over a TCP/IP link to the SMA which will relay to the EVA.


A 'BC job' is a set of predefined commands that are executed on the SMA. Apart from creating the snapshot it can automatically mount the snapshot on the backup server and start additional scripts. The BC agent on the host does the mount when told from the BC job. There is also an 'undo' function - lets not forget that the snapshot needs to be unmounted on the host and deleted from the storage array.

You cannot use the 'archive bit' to manage incremental or differential backups. A snapshot on the EVA is writable, but these changes do not get propagated back to the parent virtual disk. You might be able to implement this based on the last time the backup was run, but I don't know if your backup software can do that.

You don't sound dense to me, yet - only thorough - and that is OK when it comes to backups ;-)

[Russ_44]

Thanks to all for answering my questions. I appreciate the time you took and the thorough responses.

[Sheldon Smith]

Just to restate: When you backup a snapshot, you are NOT backing up your files; you are backing up COPIES of your files as they appeared at some point in time.
You would need a separate process to clear the archive flag on the ORIGINAL files. I have a related problem with my WinXP notebook. Two backup systems: One does a full backup but does not modify the archive flag. The other does incrementals. I created and run the attached Perl script on my notebook before doing a full backup.

[Russ_44]

Sheldon,

Thanks for taking the time to reply, and for the perl script. Netbackup 4.5 (my backup application) will do incrementals based on time/date stamps OR the archive bit -- I have to choose the method I want to use. I think the simplest solution is the time/date stamps, but if that doesn't work the perl script may be just the ticket. Thanks!

Russ