Help with Dell MD3000i, snapshots, and CentOS 5.2

Scott R. Ehrlich scott at MIT.EDU
Wed Dec 10 11:12:33 CST 2008

I have a Dell MD3000i connected to a PowerEdge 2950 server running out-of-box 
CentOS 5.2 64-bit, unpatched, on an isolated test LAN.

I also purchased the snapshot premium feature.

Using the included Modular Disk Storage Manager, I successfully activated the 
premium feature, and manually created two RAID 5 arrays + 1 hot spare.
By manually, I used MDSM instead of letting the software automatically allocate 
all disk space for me.  I deliberately selected manual and allocated 50 GB 
minus the 550 GB of each of the two RAID 5s, thus RAID 5 #1 (call it fs1) = 550 
GB - 50 GB for snapshots = 500 GB for RAID 5, 50 GB for snapshots; same for 
RAID 5 #2 (call it fs2).

Log back in to the md3000i via iscsiadm, perform an fdisk -l, and see 4 x 500 
GB partitions (2 x 500 GB per RAID 5, 2 x 500 GB per snapshot).

A few questions now -

- how do I actually create snapshots of fs1 and fs2?   What specific command do 
I use, and what specific options do I give it?  No documentation I have, 
including the index of CLI commands, gives a good enough idea/hint of this

- how do I access/view the location where the snapshots are stored/created (to 
retrieve data if needed)

- under MDSM's disk groups and virtual disks, it shows 500 GB for fs1, 500 GB 
for snapshot, and 50 GB for snapshot-repo.   What/where is the 50 GB?
Fdisk -l doesn't show it.



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