[CentOS] DatOptic RAID Array >2TB?

Benjamin Karhan simon at pop.psu.edu
Fri Jun 8 00:19:21 UTC 2007

i'm trying to set up a hardware RAID array (eRAID from DatOptic)
   under CentOS.  we have two more of these arrays which have worked
   very well for their purposes (backup and/or portable storage), but
   neither of our older arrays exceeded the dreaded 2TB barrier
   (one of them is, in fact, 2TB).
the server i'm currently testing with is running CentOS4.5, but i
   do have CentOS5 servers i could use.
the problem i'm running into is that the array SHOULD be recognized as
   ~3TB, but i'm unable (even using "parted") to see it as more than ~2TB.
   it sounds suspiciously like the typical "2TB limitation" problem, but i
   was under the impression that CentOS4 (and 5) can handle much larger (8TB?)
in fact, the kernel "USB Mass Storage" driver that detects the
   array when i plug it in only detects the device as 2TB as well.
   (so, it could easily be a limitation of that hardware driver,
   although i couldn't find any specification for that limitation
   when i googled for it).

i should say, although i dread the possible suggestions that may
   arise from admitting it, that the array also supports FireWire
   and SATA connections.  (we are STRONGLY inclined to wanting to
   use the array as USB, as our primary concern is easy portability
   and not speed)

the RAID array is the DatOptic eRAID, with 5 750GB disks in a
   RAID-5 array.  the array itself seemed to have no problem
   creating the ~3TB volume, but it does not detect as that
   size when i hook it up.

here are the relevant kernel logs:

 	SCSI subsystem initialized
 	Initializing USB Mass Storage driver...
 	scsi0 : SCSI emulation for USB Mass Storage devices
 	  Vendor: USB 2.0   Model: Storage Device    Rev: 0111
 	  Type:   Direct-Access                      ANSI SCSI revision: 02
 	USB Mass Storage device found at 3
 	usbcore: registered new driver usb-storage
 	USB Mass Storage support registered.
 	SCSI device sda: 4294920192 512-byte hdwr sectors (2198999 MB)
 	sda: assuming drive cache: write through
 	SCSI device sda: 4294920191 512-byte hdwr sectors (2198999 MB)
 	sda: assuming drive cache: write through
 	 sda: unknown partition table
 	Attached scsi disk sda at scsi0, channel 0, id 0, lun 0

and here's what "parted" also says about the array:

 	Disk geometry for /dev/sda: 0.000-2097128.999 megabytes
 	Disk label type: gpt
 	Minor    Start       End     Filesystem  Name                  Flags

it's important that we get full use of the array (1TB is a lot of
   space to waste).
anyone have any ideas, suggestions, comments, or criticisms?
any help would be greatly appreciated...

B. Karhan
simon at pop.psu.edu
PRI/SSRI Unix Administrator

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