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Sharing a 12H among 2 Servers

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Greg Stark_1
Frequent Advisor

Sharing a 12H among 2 Servers

We currently have 2 systems at one of our locations that both have mismatched, unsupported disk drives. I've ordered a used 12H with 2 controllers and 9 x 18G drives to replace all the junk and have the 2 servers share the disk on the 12H. In doing so I have a few questions I hope someone can answer:

1. One box is on 10.20 and the other 11.00, is this okay?

2. One box will initially need about 30G and the other about 20. We ordered enough disk so we have enough unallocated disk to hopefully stay in mirrored state. This will help performance, correct?

3. What is the best way to configure the LUNS for the 2 servers? I know the 12h has an 8 lun max, but is there any strategy (one big lun, 2 luns, keep luns about the same size as the actual disks) I should keep in mind as to lun size and layout?

4. Any other major considerations I should take in to account with this plan?

Thanks again,

Greg
6 REPLIES
Greg Stark_1
Frequent Advisor

Re: Sharing a 12H among 2 Servers

Oops, forgot one.

5. Since both these boxes run Oracle, is there any proven strategies for configuring Oracle file systems with regard to performance?

Thanks,
Greg
David Bell_1
Honored Contributor
Solution

Re: Sharing a 12H among 2 Servers

Greg,

I'm assuming you know that the hosts can't share the same LUNS?

In order to try to stay in the RAID 1/0 mode, the extra disk space should NOT be allocated to any LUNS.

I would normally recommend that you have at least two LUNS to be able to load balance across host HBA's. However, since you're attaching this to two hosts, you will not have the ability to use two HBA's on each host unless you're using a fibre channel MUX. Therefore, you will be using a single HBA with a maximum of 20MB/s throughput (realistic 10-12MB/s. The gain you might obtain with multiple LUNS and striping is minimal.

I would create 1-2 LUNS per host and leave some room for additional LUNS should I need to add disk.

HTH,

Dave
A. Clay Stephenson
Acclaimed Contributor

Re: Sharing a 12H among 2 Servers

Hi Greg:

David is not correct; you can connect both 12H controllers to separate controllers on each host; here's how:

HostA SCSI ID 6 ----- 12H X Controller (SCSI ID 0) ----- HostB SCSI ID 7

HostA SCSI ID 6 ----- 12H Y Controller (SCSI ID 1) ----- HostB SCSI ID 7

Note that the terminators must be installed/ enabled on each of the host SCSI controllers and two of the controllers need to be addressed at the next highest priority (6) rather than the default (7). This is actually a standard configuration for MC/ServiceGuard and will perform flawlessly.

----------------------------------------------

As for how to configure for Oracle, here goes:

I suggest that you configure 2 LUN's of equal size for each instance of Oracle (4 LUN's total).

I will talk througfh one instance but just duplicate it for your other host/instance.

LUN0 should have a primary path through controller X (alternate Y) and LUN1 should have a primary path through controller Y (alternate X). Although most DBA's will have a heart attack, you really only need two filesystems per instance and thus two LVOL's.

Create a volume group with LUN0 and use vgextend to add LUN1. Create 2 lvols (one for datafiles and indices and another for redo/archive logs. When you create the lvols, stripe across both LUN's in 64K chunks. For the datafile/indices filesystem use the vxfs mount options convosync=direct,mincache=direct,nodatainlog,delaylog; for the redo/archive filsystem use the vxfs mount options delaylog,nodatainlog. The idea is that you are going to use the raw device equivalents for the datafiles/indices and the block device (cooked files) for the archive/redo logs. Don't worry about what appears to be a bottleneck with only 2 devices - the 12H is going to split it up for up. Glance will also think that there is a bottleneck but that is normal as well; all it knows it that an awful lot of IO is going through the devices. As mentioned, leave as much unconfigured space as possible on your 12H (50-55% total usage is great; you will stay in RAID 10) and if you have 10K RPM drives so much the better.

Striping across both external paths will fully utilize both external SCSI busses.

I've attached a paper I wrote for my Jr. Admins that explains how to set up 12H's in MC/SG environments. As long as you ignore the vgimport and MC/SG vgchange stuff everything applies.


Regards, Clay

If it ain't broke, I can fix that.
David Bell_1
Honored Contributor

Re: Sharing a 12H among 2 Servers

Clay,

Thanks for the correction. I was assuming a non MCSG configuration. With the inline terminators and different SCSI ID's, can the LUN's be shared without MCSG. I know if one is Read Only, however, can they both be utilized with full functionality?

Thanks,

Dave
A. Clay Stephenson
Acclaimed Contributor

Re: Sharing a 12H among 2 Servers

No David, I was not referring to your first point but rather your second point about being able to use only one HBA per host. LUN's cannot be shared across hosts but LUN0 and LUN1 could be used by hostA wile LUN's 2 & 3 could be used by hostB.
LUN0 and LUN2 can be primary controller X while LUN's 1 & 3 can be primary controller Y.

This way both hosts can utilize 2 external SCSI paths to the 12H. Of course, at some times there will be contention but this is a normal and expected condition on a SCSI bus and the systems will handle it transparently.
If it ain't broke, I can fix that.
David Bell_1
Honored Contributor

Re: Sharing a 12H among 2 Servers

Clay,

Thanks for the clarification. I appreciate your insight and providing an educational lesson. I'll remember this when I have an opportunity to award points.

Thanks Again,

Dave