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.

[j bohg]

Hey there, I'm still a bit confused about the whole thing. I understand why we only have 1,43Tb of free disk space, that comes from using a spare in our configuration. Is it wise to make a new configuration without using an spare? And what is the difference between a Spare and a Hot Spare?

[Uwe Zessin]

It depends on how much value you put on the availability of your data (no, I'm not trying to be funny). A spare disk will immediately be used to rebuild redundant information when a disk drive has gone bad.
Otherwise you have to monitor your system and manually swap the disk. You do have an unused disk lying around? Can you afford to run without RAID protection until a replacement part has been shipped to you?

(hot) spare or not. I've once read the definition that a 'hot' spare is already spinning while a 'simple' spare is not.
Unfortunately, different arrays use different terminology and these days disk drives are starting automatically anyway. By that definition, all spares are 'hot'.

[j bohg]

Many thanks for all the answers. It certainly helped me out a lot and things are a lot clearer to me.

Stil one question left and that is why I see two new identical drives in Windows Explorer with the same amount of free space but different drive-letters. I just did a complete new configuration and deleted the old one. As soon as I assigned a drive letter to the logical drive in Disk Management the two drives became visible. In disk management only one disk is visible. Any explanation would be helpful.

[j bohg]

I'm still confused about the two disks in the Explorer. Last night I did a new test on the logical drive, wich I called drive R in Disk management. I created a folder on the disk and somehow it seemed to be mirrored to the other disk. Question is how can it be that I see two identical drives, both with 2Tb, while I only have one logical drive with a 2Tb capacity.
When opening properties I noticed that the server sees two logical volumes while only having one. I included a screenshot from this. It says that write caching is enabled. Could this be the reason, that the server created one drive for caching? Would that also be the reason that I cannot see the second drive (I) in disk management?

[Uwe Zessin]

Very strange. It _looks_ like there are two paths to the same data, but I don't see how this is possible in your configuration... Is there some add-on software that can create block-based snapshots?

Is there anything interesting in the Windows Event Log?
Can you attach the output from the following command as a text file (no Word document ;-), please?
+----
C:\>reg query HKLM\HARDWARE\DEVICEMAP\Scsi /s > scsi_%COMPUTERNAME%.txt
----

[j bohg]

Thanks for your reply Uwe, I looked in the event log but couldnt find anything usefull. I attached the file you requested and hope it is usefull. Thanks in advance!

[j bohg]

Hey Uwe, as you requested I attached the txt file in my previous reply. If you have a spare minute I would really appreciate it if you could run through the document to see if there's anything wrong.

many thanks in advance!

[j bohg]

Perhaps there is someone else who understands the output in the attached file? Any help would be greatly appreciated.

[Uwe Zessin]

I'm sorry, I have lost track of this thread - thanks for the reminder...

There a two disks which are seen through the same controller port:

HKEY_LOCAL_MACHINE\HARDWARE\DEVICEMAP\Scsi\Scsi Port 5\Scsi Bus 1\Target Id 0\Logical Unit Id 0

HKEY_LOCAL_MACHINE\HARDWARE\DEVICEMAP\Scsi\Scsi Port 5\Scsi Bus 1\Target Id 1\Logical Unit Id 0

Can you open the device manager and use [View->Devices by connection]? This gives a hierarchical overview. I'll attach a picture with an example drill-down.

[j bohg]

Hey Uwe, great to hear from you. I understand that you cant keep track of all treads. Thanks for your reply, I attached the image you requested. Hope this will make sense.

[j bohg]

Uwe, hopefully you can find some time to respond to the file I uploaded last week. Maybe you lost track again witch is understandable. Anyways, your help is greatly appreciated so hope to read from you soon.

[Uwe Zessin]

Hello,

I've tried to understand the data, but I have some problems as there are some inconsistencies:

The picture that you uploaded on Sep 2, 2008 12:14:41 contains two parts. In the upper part, the Disk0 contains 4 partitions, but they don't have drive letters assigned to them.

However, the screenshot from Sep 2, 2008 11:46:31 shows 4 drive letters (C:, D: E:, F:), which I guess belong to Disk0.


The SCSI device map and the screenshot from the device manager show that there are two disk provided by the SmartArray 6400 (scsi5), but they don't seem to be visible in the screenshots from Sep 2, 2008 12:14:41 GMT.


Can you provide an ACU screenshot similar to the one from Sep 2, 2008 11:46:31 GMT, but this time choose the SmartArray 6400?

[j bohg]

Good morning Uwe, thanks again for your reply. Again I attached some screenshots from our server. I hope this covers what you requested and hope to read from you soon.

[Uwe Zessin]

Wow, that is a cool screenshot ;-)

It looks better now, lets see if we can get some more details. Could you please execute the following commands, store the files in a folder and put everything in a .ZIP file?

wmic diskdrive > diskdrive.txt
wmic logicaldisk > logicaldisk.txt
wmic partition > partition.txt
wmic shadowcopy > shadowcopy.txt
wmic shadowstorage > shadowstorage.txt
wmic volume> volume.txt

[j bohg]

Hey Uwe,

[Wow, that is a cool screenshot ;-)]

Yes, we have 30 inch monitors turned 90degrees sideways :)

I'll gather all the information again and keep you posted!