LUN size on MSA1500cs

[Raymond Krystofolski]

MSA1500cs with 4 SATA enclosures with (8) 259GB SATA disk drives in each enclosure.
(8-250GB)disks/enclosure x (4) enclosures, or
(32)x 250GB = 8000GB or 8TB.
Using Windows 2003 Enterprise, what would be the largest LUN that could be created using;
- raid 5 on MSA1500cs?
- raid ADG on MSA1500cs?
Is there a limit under the MSA1500cs as to how many disks can be in an array?

[John Kufrovich]

Windows limit 2TB
MSA limit 2TB LUN size. Regardless of RAID level.

No maximum on the number of disk per array. The more drives in an array the better the performance BUT increasing the drive count increase the likely hood of array failure. MTBF for SATA is around 500000 hrs, divide this by the number of drives in your array.

[Uwe Zessin]

To add to John's message...

you can create multiple logical disks per disk array, although the handling can be a bit tough. At least on the MSA1000 you can only delete them in reverse order of creation and I doubt the MSA1500 works different.

The MTBF goes down if more disks are used in an array, but one usually does not use RAID-0 and this rule applies to all storage arrays. With the bad MTBF of SATA disks it is better to use ADG pretty early. If I recall correctly, one should use ADG when one starts to use about 14 SCSI disk drives per disk array, but I don't remember the value for SATA disks.

[Dean Simiana]

You are effectively limited to a max. of 2TB per lun due to limitations with the SCSI protocol. (this is entirely OS independant.)
My understanding is:
The SCSI command protocol, SBC-1, is 32bit, reulting in a limit of 32bit logical block addressing with 512byte block size.
I believe that HP will address this with the Serial Attached SCSI devices and the SBC-2 protocol that is under development.

In Windows 2003, you are also limited to 2TB basic disk size, but can use Dynamic 2TB disk volumes and Span volumes, although personally I'd try to avoid doing so as it is impossible to incrementally undo and may pose a problem in your future; personal preference.
You may find these usefull:

http://www.scsita.org/aboutscsi/sas/tutorials/SAS_SCSI_upper_layers_public.pdf

http://www.microsoft.com/resources/documentation/WindowsServ/2003/all/deployguide/en-us/Default.asp?url=/resources/documentation/WindowsServ/2003/all/deployguide/en-us/sdcbc_sto_cokp.asp

[Steven Clementi]

Too add some more bad news.... if not already figured out...


SATA drive MTBU(MTBF) is usually measured at a 20% to 30% duty cycle vs. SCSI drives being measured at 70% to 80% DC.


What does this mean? If a SATA drive is measured at about 500,000 hours and 20%DC... your drives should be doing alot less work then if you had a SCSI solution.

What will you be using the storage for?


Steven

[Joseph Rehling]

On correction to a post I read. Windows is limited to 2 TB on a basic partition, but you can do up to 256TB on a GPT partition. The MSA1500cs is the limiting factor to the size of the GPT. I know HP is working on larger volumes on the storage side. The P800 appears to be the first controller by HP to support above 2TB. For the record... I have a 25 TB partition on another vendors SAN, but you would not want to run check disk on that volume (could take days). This was done with a GPT partition in Windows... Very stable for close to six months, but it appears to be much more stable than the 6TB volume we have using Dynamic disks (2 hours for a check disk on that volume). Microsoft is working to fix ChkDsk in Long Horn so that ChkDsk can fix problems without taking the disk off line, but there is no way to be sure they will be able to deliver that... I have a vested interest in this type of information, so if you find that my data is wrong I would live an update so I keep current.