Equallogic Storage Pool Assignment Satisfaction

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During an array migration usually you can use application level trick to move your data between the old and the new array. For example with VMware vSphere you can use the Storage vMotion features (now added also in lower edition of vSphere 5.1) or with Microsoft Hyper-V 3 you can use the new Storage Live Migration feature.

But in some case you may have also an option at storage level. For example to migrate across two Dell EqualLogic array (also different models) you can use the embedded function.

The trick its simple: just add the new EqualLogic as an additional member in you existing group (a group must always exist, also with a single member). Note that you need a minimum firmware level compatibility and usually is recommended have the same firmware level in all members of your group.

At this point when you enter in the web interface and click on the new array you have a pop-up asking to initialize the disks. Be sure to choose the desidered RAID level (remember that you can live move from RAID10 to RAID50 to RAID5 and that for SATA a RAID6 level is recommended) and a new storage pool.

Each EqualLogic volume (or for other storage, each LUN) is stored on a single storage pool, as you can easy see in the volume properties.

Note that a storage pool can be across more members, in this way we can have a distributed volume (in a configuration similar to a RAID0 over the network and with some auto-tiering features).

Now you can the pool and migrate your volume, by simple change its properties and the desidered storage pool! The data migration across pools (that means also across arrays) will be start as soon is possible.

It’s really easy and works at volumes level. You can make this changes on more volumes, but all those operations will be serialized in one by one.

You can monitoring (and if needed also aborting) the operation at volume level, or at group level (in the operations pane).

When all volumes have been migrated and the old storage pool is empty you can remove the old array(s) from the group (note that you can remove an array also with data on it, and the software will automatically migrate the data, but I prefer the manual migration to have more control). Now you can use the to build another group, for example for a disaster recovery site.

The main benefit is that this operation is completely at storage level without any resource consumption at storage level (although with VMware VAAI or Microsoft ODX you can mainly offload a VM data migration across datastores).

Another advantage is that is complely transpared with no needs of any reconfiguration (or new volume presentation) at host level.

This kind of migration can also preverve all storage property at volume level, like storage snapshots, storage replication, schedules and so on.

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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)

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