EMC Replication Technologies – Simplified Guide

From a DR standpoint, using replicated SAN’s to provide a fully functional DR site is nothing new but was usually a fairly expensive endeavor especially for smaller organizations.  Now, as SAN prices have come down and technologies like VMware Site Recovery Manager are making replicating data for DR more automated and reliable, more and more organizations are taking a serious look at replicated storage solutions.

Being as we are an EMC Partner I’ll concentrate on some of things to think about when considering a replicated SAN infrastructure.  EMC has many ways to replicate SAN data.  Here is a short list of some of the technology and where they’re used:

-          MirrorView:                      

• MirrorView is used on Clariion and Celerra arrays and comes in two flavors, /A – Async and /S – Sync.

-          Celerra Replicator:         

• Used to replicate data between Celerra unified storage platforms.

-          RecoverPoint:                  

• Appliance based Continuous Data Protection solution that also provides replication between EMC arrays.  This is commonly referred to a “Tivo for the Datacenter” and is the latest and greatest technology when it comes to data protection and replication.

Each of these replication technologies replicates LUNS between arrays but they have different overhead requirements that you should consider.

MirrorView

-          MirrorView requires 10 to 20% overhead to operate.  So if you have 10TB of data to replicate you are going to need an additional 1 to 2TB of storage space on your production array.

Celerra Replicator

-          Celerra Replicator can require up to 250% overhead.  This number can vary depending on what you are replicating and how you plan to do it.  This means that 10TB of replicated data could require an additional 25TB of disk space between the Production and DR arrays.

RecoverPoint

-          While RecoverPoint is certainly used as a replication technology it provides much more than that.  The ability to roll back to any point in time (similar to a Tivo) provides the ultimate granularity to DR.  This is accomplished via a Write Splitter that is built in to Clariion arrays.  RecoverPoint is also available for non-EMC arrays.

-          RecoverPoint can be deployed in 3 different configurations, CDP (local only/not replicated), CRR (remote) and CLR (local and remote).

• CRR replicates data to your DR site where your “Tivo” capability resides.  You essentially have an exact copy of the data you want to protect/replicate and a “Journal” which keeps track of all the writes and changes to the data.  There is an exact copy of your protected data plus roughly 10 to 20% overhead for the Journal.  So 10TB of “protected” data would require around 11 to 12TB of additional storage on the DR array.
• CLR is simply a combination of local CDP protection and remote CRR protection together.  This provides the ultimate in protection and granularity at both sites and would require additional storage at both sites for the CDP/CRR “Copy” and the Journal.

This is obviously a very simplified summary of replication and replication overhead.  The amount of additional storage required for any replicated solution will depend on the amount, type and change rate of data being replicated.  There are also many things to consider around bandwidth between sites and the type of replication, Sync or Async, that you need.   EMC and qualified EMC Partners have tools to assess your environment and dial-in exactly what is required for replication.

Flash Drives – Solid State Drive Technology for your SAN

Every once and a while at client meeting the discussion about Flash Drives or Solid-State Drives (SSD) comes up.  Flash drives are now an option in EMC’s Clariion arrays.  Usually the first question is “I heard they’re expensive, what do those things cost anyway?”  Well the short answer is A LOT.   Retail from EMC is over $15,000 each!  Yeah….I’ll take a few trays just in case we need some extra storage space!

Obviously you wouldn’t purchase this type of storage to store your MP3 collection but what are the benefits and use cases for these drives?  According to EMC the new Flash Drive technology is for Tier Zero apps or in other words, applications that require incredible amounts of disk I/O and performance.  Examples of this could be some SQL and Oracle production databases.

So why use Flash Drives?  Marketing numbers from EMC state “up to 30x the IOPS” of a standard drive can be achieved.  Let’s be conservative and say 15x IOPS for the purposes of this example.  If you had a database the generated, let’s say 10,000 IOPS, you would need to stripe that data over at least 55 drives to achieve the performance needed (assuming 180 IOPS/drive).  With Flash drives you could theoretically do it with as little as 4 or 5 drives or even less.  Of course with a maximum drive size of 73GB per drive, space might be an issue.

Here is a brief summary of the benefits of these new drives:

-          More Performance:        At up to 30x IOPS of a normal high-speed drive you can reduce the number of spindle you need and increase performance.  Latency is also dramatically reduced

-          Greener:                             The drives use much less power because there are now moving parts which translates in to less heat, less cooling a smaller carbon footprint and more financial savings.

-          Higher Reliability:           No moving parts equal less to break as well as much faster rebuild times.

-          Less Rack Space:               Using less drives will free up rack space and datacenter floor space.

The obvious drawback to these drives is cost.  Most companies with tight budgets will have a hard time justifying the astronomical cost per megabyte that comes along with this technology.  For some high-performance apps though, they may be a great solution.  Hopefully with time and competition the cost will come down and the usable space will go up.