Getting the next generation disk array from HP and I'm trying to figure out the best way to configure it. The EVA has a new concept called "disk groups" that I just can't get my hands around. The lowest level of storage that the EVA uses is a Redundancy Storage Set (RSS). The EVA basically groups your disks into these RSS's based on the number of disks in your disk group.
The "disk group" basically sits on top of the RSS and is a logical collection of disks. The disk group is stiped across all disks in the disk group. Each "virtual disk" (basically LUN) is then created from a single disk group and assigned a "vRaid" level. You can create as many "vDisks" in your disk group as you need. A single vDisk can not span multiple disk groups unless you use a LVM like vxvm.
The documents I'm reading (here, and here) are conflicting at best. One says that a database server should have one disk group effectively implementing SAME (stripe and mirror everything) for you. The other document says to configure the number of disk groups for the type of I/O you will encounter. Knowing that the redo logs will be sequential access and the datafiles will be a mix of random and sequential access, I think there should be at least two disk groups.
Performance wise, every fiber of my being tells me one filesystem just isn't going to cut it no matter how many physical disks are under it. Do I really want all 48 disks spinning for a 8k write?
One of my fears is that if I lose a disk group, I lose everything. HP, of course, says you will never lose a disk group. Experience on other HP products tells me the first time we have a failure, we'll get some bad advice and wipe something out. Am I just being paranoid about losing a disk group?
Does anybody have practical experience on HP EVA's that can offer some insight?