topic Re: Help with SC10 connection in Disk Enclosures

Help with SC10 connection

Pocius Arturas — Mon, 25 Aug 2003 05:02:22 GMT

Hello,
We have two L1000 hosts with two LVD SCSI on each.
Also we have two SC10 boxes with two BCC's on each. SC10 disks used for Oracle data.
What the best way to connect them to make the most high availability system?

Thank you.

Re: Help with SC10 connection

Bernhard Mueller — Mon, 25 Aug 2003 12:21:58 GMT

Hi,

you could set the SC10s in full bus mode (DIP switch setting see manual) and connect each SC10 to a SCSI card, which requires that you change the initiator target id from 7 (default) to 6 for two of the cards.
(need to reboot change at BCH in service menu with scsi command)

Then each L1000 would see all the disks in both SC10 and you could mirror from one SC10 onto the other using PVG-strict mirroring.

That would be a typical config for use in MC/SG. assume you plan to setup a cluster?

Regards,
Bernhard

Re: Help with SC10 connection

Pocius Arturas — Tue, 26 Aug 2003 05:04:50 GMT

Hi,

No, not using MC/SG at the moment.

Re: Help with SC10 connection

Pocius Arturas — Tue, 26 Aug 2003 05:05:11 GMT

Hi,

No, not using MC/SG at the moment.

Re: Help with SC10 connection

Peter Mattei — Tue, 26 Aug 2003 06:35:19 GMT

If you are using independent servers I strongly recommend to use both SC10 in Split-Bus mode. See the first configuration in my attached document showing the different modes.

This will isolate half of the disks to either and half to the other BCC.
Otherwise you could mount and damage the other servers disks/data!

Cheers
Peter

Re: Help with SC10 connection

Peter Mattei — Tue, 26 Aug 2003 06:38:30 GMT

The attachment got corrupted so I try it again!
Peter

Re: Help with SC10 connection

Pocius Arturas — Tue, 26 Aug 2003 09:27:58 GMT

But before mounting disks, it's
necessary to create logical volumes at first.

So, maybe it's not so big thread for
corrupting volumes already mounted on the
other server?

Or it's something else?

Thank you.
Arturas

Re: Help with SC10 connection

Peter Mattei — Tue, 26 Aug 2003 10:10:27 GMT

Well, if a server "sees" the targets of the other it can thoretically issue SCSI commands to it and corrupt data.
You can also import the logical volumes of the other instance.
This is exactly what ServiceGuard does if it takes over. But in addition ServiceGuard acts as an arbitrator to only allow one server to access the volumes at a time!
So you can run without seperating the disks but you are prone to human errors.

Cheers
Peter

Re: Help with SC10 connection

Pocius Arturas — Tue, 26 Aug 2003 10:19:24 GMT

What impact ServiceGuard does on performance of such system?
Is it significant?

Thank you.
Art??ras

Re: Help with SC10 connection

Pocius Arturas — Tue, 26 Aug 2003 10:21:51 GMT

What differences are in performance to
compare SC10 split and full bus modes
(as shown in attachments).

Re: Help with SC10 connection

Peter Mattei — Tue, 26 Aug 2003 11:15:30 GMT

ServiceGuard has almost no impact. It just takes some monitoring and heartbeat cycles of your server.

In a split Bus environment you isolate SCSI and therefore the IOs, so the servers cannot impact each other.
Anyway, in a "normal" environment you will hardly be able to notice a difference.
The more important thing is the number of disks in a volume group!

cheers
Peter

Re: Help with SC10 connection

Pocius Arturas — Tue, 26 Aug 2003 12:24:19 GMT

Can you explain your last sentence?

Re: Help with SC10 connection

Peter Mattei — Tue, 26 Aug 2003 13:54:14 GMT

Well, a single disk with 10k rpm can do 100 to 150 read-IO operations per second.
If you let's say have 20 disks, mirrored with Mirror-UX and build a volume group and spread your accesses over all disks you will have 10*100 to 150 = 1000 to 1500 read-IOs max. you can expect.
Doubling the number of disks will theoretically double the IOs you can achieve (also depends on connections, saturation of SCSI bus etc)

Peter

Re: Help with SC10 connection

Pocius Arturas — Wed, 27 Aug 2003 04:28:15 GMT

Thank you for the help.

Arturas