How to configure disks for databases and logs

I am planning out the disk configuration for our Exchange 2007 server. It has a SAN back-end. I want to create LUNS for our Storage Groups and Databases. I will have four Storage Groups with one Mailbox Store in each Storage Group. I was going to put all Databases on a single LUN because that is the way our Exchange 2003 server is configured, but with or current server, I have only 1 Storage Group. Should I create a separate LUN for the log files for each Storage Group, or can I put all the logs from all 4 Storage Groups on the same LUN. It seems easier to put them all on the same LUN so I don't have so many different drive letters to deal with. Just wondering what everyone else is doing.

Thanks
osiexchangeAsked:
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SteveH_UKConnect With a Mentor Commented:
Another advantage of using separate LUNs would be to allow online migration of a LUN to a different storage device.

However, although I understand the disk issues, I have little practical experience of SANs so another expert's advice would be welcome.
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SteveH_UKCommented:
You might want to read http://msexchangeteam.com/archive/2006/04/07/424645.aspx

There isn't a real issue with combining the disks that hold data, as this is all random access.  Except, of course, if you want to backup them separately.

The logs would benefit from being on separate LUNs, but it really depends on the number of disk platters available, and therefore cost.
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osiexchangeAuthor Commented:
Thanks for the articles. I will take a look at them. Our Raid groups on the SAN use a Raid 5 utilizing 8 physical disks. The only reason I did not want to go with separate LUNS for each Storage Group log disk is because it would create multiple drive letters which can get confusing.
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SteveH_UKCommented:
Agreed, but Exchange 2003/7 also support direct storage on SANs which performs better than file based approaches.

I'll look up the references...
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SteveH_UKCommented:
My mistake, you map them to a drive!

Are you using an iSCSI initator?
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osiexchangeAuthor Commented:
Yes, ISCSI initiator. Each LUN shows up as a drive letter under Windows. The more I think about it, having all the logs from all the Storage Groups go to a single LUN is not much different than what I am doing now only with local storage. I have a single Storage Group with 4 Mailbox Stores. All the logs for all 4 Stores go to a single spindle. The databases go to a separate spindle. I would think the advantage would be better performance however is each Store had its own log file LUN to write to. I'll check out that article.
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SteveH_UKCommented:
I guess it depends how many spindles you have in your LUNs!

Use RAID1 or RAID10 for the logs.   Use RAID5 or RAID10 for the data.

Whether you grow a LUN by extra spindles, or split the data/logs across more LUNs is up to you, but I would recommend the former as it will be easier to manage for changing environments, i.e. keep LUNs to store different types of data with differing access patterns.
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osiexchangeAuthor Commented:
Thanks. I am still not clear on whether to break out separate LUNs for log files and data stores. I think if we want to use LCR, we need to. With Four storage groups and a store in each storage group, that would be 5 individual drive letters if I put all the stores on a single LUN and 8 drive letters if I break out the stores to separate LUNS. FOr LCR, I can use mount points but still, 8 drive letters seems ridiculous.
I was just wondering what other people are doing.
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SteveH_UKCommented:
You don't have to mount partitions at the drive letter level, so I'm not sure why you need so many drive letters!

What I recommend is that you create a logical disk structure within a folder, perhaps in C:\SANDisks, and then map individual LUNs to folders within there, optionally using another level of structure to represent the type of data.

You can do this logical mapping in Disk Management.
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