September 8, 2011 at 8:09 am
Hi,
I am new to the hardware side of database administration and i have some questions about the existing set up of one of our old servers.
The server in question has two RAID arrays and only one RAID controller (as stated above) but the controller has two virtual disks created on it. The virtual drives do not seem to be mapped to specific RAID arrays as far as i can tell.
For all intents and purposes, it looks like the server has two drives and the current set up stores data files on one of these drives and log files on the other.
My question is, because both drives (and both RAID arrays) use a single RAID controller; are we actually locating the log and data files on seperate arrays and benfiting from the seperation at all?
I apologise if i am not making my question clear enough, please advise if more info is needed.
Thanks.
September 8, 2011 at 8:12 am
The physical separation on drives is more important than the controller. While you could saturate the controller's bus, usually you get more bottlenecking on the drives themselves. You'd have to compute the throughput of the two arrays (drive specs and config) to determine if you're saturating the controller.
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September 8, 2011 at 8:33 am
Thanks for the prompt reply, i'm not sure that i follow you here but i dare say i havent made myself very clear. Let me try again.
We are experiencing high "% disk time" and "sec/write" counters on the server in question; i have read that one cause could be a problem with the disk storage (the server has sufficient memory and there are no signs of processor overuse).
I investigated further to see that we have two RAID arrays connected to one controller which has two virtual drives. Whoever set up this server was probably working under the assumption that storing data on one drive and logs on the other would be more efficient because they would be kept seperate.
Here is my assumption, please tell me if i'm wrong:
Because these are actually virtual drives which are not mapped to a specific RAID array they will not be seperated and all data and log files will be written across both arrays that are connected to the controller.
September 8, 2011 at 8:38 am
If the data and logs aren't separated physically, then you could have an issue. I haven't worked with virtual drives. Typically you would have two arrays from one controller (or 3, 4, etc) with the logical drives being separated.
If that's not the case, then you might have contention.
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September 8, 2011 at 9:31 am
Thanks again for your help.
The whole creation of virtual disks is really confusing me, i really dont follow how they relate to the RAID arrays.
I'll continue looking online.
September 8, 2011 at 9:58 am
My guess is the virtual disk is a layer on the array, but hard to know. Sounds like what SAN people do sometimes.
Post back if you learn something. Curious to know what is happening here.
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September 8, 2011 at 10:09 am
Upon further inspection, the virtual disks do indeed have physical disks from the two RAID arrays "mapped" to them and these then appear as the C and D drive on the server. This is set up within the BIOS config utility.
As previously stated, i'm a newcomer to this so i'm still finding myself around the management console.
Thanks for your help.
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