MSA20 RAID 5 two identical drives

[j bohg]

We recently installed a MSA20 with 4x750Gb configured it to a RAID 5 solution and created one logical drive wich has 143Gb capacity. First this we notioced was the 143Gb capacity wich seems odd. We installed 4x750=3000Gb. What happenend to the rest of our Gb's?

Second thing is that having one logical drive we assumed to see only one drive-letter in windows explorer. We assinged the letter X to our drive but we also see a second drive with the letter I. The two drives have the exact same capacity and if we store files on one of the drives they apear on the other drive the day after. They weird thing is that we cant seem to delete/remove the second drive, it also doenst appear in Disk Management on the server (Small Business Server2003). Could anyone explain why this second drive appears and how to delete/remove/hide it?

All help is appreciated.

[Víctor Cespón]

First, since the early days of hard disks, the manufacturers report the capacity in powers of 10, not powers of 2. So 750 GB are 750 billion bytes approx.
In powers of 2, this would be 750/(1.024)^3 = 698.5 GB.
Second, the logical unit that you created was filling all the disk space available?
Third, this MSA20 is connected directly o a server or though a MSA1500?
The MSA20 has only one SCSI connector and disks should be seen only once by the server.

[j bohg]

Thanks for the reply. We have our MSA20 connected to the server via a Smart Array Controller 6400. I hope this will help in seeking answers to my questions.
As far as the capacity, I dont think I really understand what you are trying to say with:

"Second, the logical unit that you created was filling all the disk space available?"

Could you please clarify this. Do you mean that the MSA20 only supports 2Tb of space while we have 3Tb so all disk space is filled?

[Víctor Cespón · Accepted solution]

If you create a RAID with 4 x 750 GB disks, you'll have 2794 GB of RAW space, which will allow you to create a 2 TB RAID 5 logical unit.
Did you create a logical unit using all the available space or a smaller one?
The connection to a SmartArray 6400 is correct, in this case the RAIDs are created on the MSA20 and the SmartArray is only the bridge to the server.
Can you attach a capture of the ACU screen showing what you have created?

[Uwe Zessin]

> Do you mean that the MSA20 only supports 2Tb of space

No, the size of an individual logical disk is limited to 2TB. The MSA20 has an U320 SCSI interface which cannot deal with LUNs larger than 2TB. However, you can create another logical disk from the remaining space.

[j bohg]

I've attached an image of the ACU and a screenshot from our Explorer on the server. I've marked the MSA drives with a red arrow.

> Did you create a logical unit using all the available space or a smaller one? <

At the time of configuring the MSA I didnt now there was a limit so as far as I know we tried to attach all available space.

[Víctor Cespón]

You have set one drive as spare, so you lose 750 GB for parity and 750 GB for a spare. 1430 GB is the correct size in this case.

Now, can you attach a screenshot from device manager - disks, and from disk manager?

[j bohg]

Many thanks for your reply. Things are starting to make sence now, except for the two dives in the Explorer. I've attached the screenshots you requested.
We assigned a spare because it was recommended during configuration of the array. Do you know if a spare really is nessecary?

[Víctor Cespón]

The device manager sees only 2 disks, one is the internal to the server and the other is the one from the MSA20.
This is confirmed on the disk manager, disk 0 of 273 GB, and disk 1 of 1397 GB.
There are 5 storage volumes, 4 partitions in the internal disk and 1 on the MSA20, so you should have 5 drive letters assigned to disks.

Drive I: is not being assigned from disk manager (disk 1 = X:). So you'll have to investigate in Windows where does it come from.

[j bohg]

The weird thing is that any data that is stored om drive X, will automatically be put on drive I as well. Both drives have the same sorage capacity of 1,36Tb. As soon as wel created the drive X, wich we called MSA they I-drive appeared as well.