ethrbunny,
The VMware community post you mentioned in your edit is a bit outdated... Dell Equallogic recommendations for RAID policy are laid out in the Choosing a Member RAID Policy document though.
With 24x600GB disks, it's presumable you'll be using either 10K or 15K SAS drives. If that's the case, RAID 6, 10, and 50 are the recommended options. In accordance with what tim mentioned, an Equallogic storage array with 24 drives only lets you chose one RAID type/policy for an enclosure; the actual RAID sets are managed by the array on the back-end with no real user visibility through the GUI. Due to the number of drives, you're correct in being wary of having that many drives in a single RAID set, which is why the array splits them into two separate RAID sets (which is both better for data protection/redundancy and performance).
RAID6 is by far the best RAID policy to select for data protection, assuming that you have the system in warranty and drive failures will be dealt with promptly rather than ignored. The aforementioned document details the statistical likelihood of data loss between the different policies available, and RAID6 is a clear win by this measure.
Performance-wise, RAID6 suffers greatly with random writes in comparison to RAID10. It also experiences a greater performance impact during a failure/rebuild in comparison (though this is almost entirely negated with the copy-to-spare operation introduced with new firmware revisions for handling of preemptive failures).
If your current storage solution incorporates 16 or fewer drives of the same or lesser speed, I would nearly guarantee that a RAID6 policy would provide ample performance and IOPS for your needs in addition to the best capacity and protection level you can get on that array.
However, you could also consider setting up all of your volumes with thin provisioning, and allocate a max capacity for each volume that give you plenty of room to grow (even if that means over allocating to some degree). Start with a RAID10, get your full production environment in place, and then use the SAN Headquarters software provided by Equallogic to measure your performance (feel free to contact support or a technical sales rep for more info on this - they're usually very helpful). If your IOPS on individual drives is sitting below 100 even at your peak utilization, then you can easily get away with converting to a RAID6 to gain some extra capacity. The catch to this is that you cannot convert back from a RAID6 to a RAID10 without performing a factory reset on the array (which is only realistic in large multi-member environments) so make sure to do your research before making the switch.
Summary
RAID type recommendation: RAID 6 (verify this w/ Dell after having your capacity needs evaluated)
Volumes: 4TB volume for your database + 3+ volumes (perhaps 2TB in size) for VMFS datastores (multiples recommended for various performance reasons), all with thin provisioning enabled
Note 1: RAID10 on this array would give you just under 6TiB of actual usable capacity, while RAID6 would give you just over 10TiB (possibly a touch lower for each after space taken up by array's metadata)
Note 2: These recommendations are all assuming you don't plan to make much use of the replication or snapshot features. If you do, you'll need to take the additional space requirements into consideration as well (making RAID6 an even more favorable option)
Best Answer
it’s Joe with Dell EqualLogic.
The EqualLogic arrays utilize all available disk space on the member for the RAID set. So, you can only have one RAID policy per member. There is no way to shrink the size of the RAID set, and create another RAID set on a single member.
You have two options;
1: As you surmised, since this is a single member group, you would need to remove the data from the array, than remove the member from the group. But, since this is a single member group, when you remove the member, you would in fact, destroy the entire group (all volumes, settings, IP’s, SMTP, SNMP, ACL’s etc.).
When removing a member from a single member group, you would first need to capture all the group information.
Once the member is deleted from the group, when you recreate the group (and the member with the RAID-50 policy), you would need to re-input all the settings.
You can do this manually, or use the "save-config" command prior to destroying the group: The save-config command can be run in default or group-only mode.
In default mode, the resulting file will automatically restore the following:
If you specify the save-config command with the -grouponly parameter, member and pool configuration information will be saved as comments instead of commands, so you must manually restore these parts of the configuration. A member’s RAID level and pool must be selected before you can use the storage.
The save-config command will not restore the basic member network configuration or the group configuration, but it will save this information as comments in the restoration file. The following information must be manually supplied to each member by running the setup utility:
2: The second option requires a second EqualLogic array (contact you sales person to see if they have a loaner you can borrow).
If you have a second array, you would first create a second storage pool in the group (initially it would contain no members). Once the pool is created, you would then initialize the second array AND add this array to that new pool.
Once the new member is added, move the volumes from the existing member (in the default pool) to the new member (this will take some time depending on the amount of data, network, etc., note that this can be done while the array is serving up data, so there is no downtime during this process).
Once all the volumes are vacated from the original member, you can then remove the original member from the group (delete member), and reconfigure it to RAID-50, and add it back into the group in the same pool it was removed from (do not add it to the pool with the loaner/spare member).
Once the original member is back in the original pool, you can then move the data from the 2nd array back to the original member (again, this can be done without downtime).
Once the data is moved back to the original member, you can remove the loaner/spare member.