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Storage Efficiency – Storage Tiering

In a traditional Storage allocation model, Storage Requirement for most environments are typically satisfied by allocating the Storage based on the Capacity requirement rather than Performance because of either not knowing the Performance requirement of the application/environment during its initial deployment phase or due to lack of understanding of the importance of RAID and associated Disk penalties.

Consider this, if there is a requirement to host 500 VMs of 18 IOPS each and 100 GB Capacity, We are looking at a Storage requirement of 6 TB (5 *100 GB + 25% Buffer Overhead) & 9000 IOPS. Considering a Read:Write ratio of 70:30 in RAID 5, we are looking at IOPS Requirement of 17100 which can be satisfied by 95 numbers of 15K drives. Consider RAID 5 configuration with 4+1 Drives for these 95 drives to satisfy the IOPS Requirement, We would be left with roughly 38 TB of Usable Space. But our capacity requirement was only 6 TB. How do we satisfy the IOPS and still right size for Capacity or how do we size for Capacity and still match the IOPS Requirement? Are we not spending additional $$$ to accommodate Performance requirements when most of the virtual workloads would not be active all the time?

Storage Tiering is recommended when you want maximum Efficiency at lower cost. Simply put, automating data migration/placement within different tiers of storage according to workload. If we consider the same example referred above, instead of placing in 95 numbers of 600 GB drives, Can we look at an alternate approach of using multiple drive types in a Single Storage Pool like 5 numbers of SSDs along with 27 numbers of 900 GB 10K SAS plus 16 numbers of 2 TB  NL-SAS. SSD & SAS Drives would serve the performance requirements whereas the NL-SAS would serve the capacity requirement at lower cost. Active data set within the pool would be automatically migrated to SSD/SAS drives whenever they get active and inactive data would get into the NL-SAS drives. There are a lot of advantages in this model since you can keep expanding your Storage Pool with additional drives as and when required online. Data placement would be handled automatically by the Storage Array and with Powerful SSD based Cache that are available these days, Storage Tiering is the way to move forward for high-capacity environments.

For VMware Environments, you have an additional choice of enabling and making use of SDRS in cases where Storage Array doesn’t have the capability or licenses for Storage Tiering. This can also do a limited level of automatic placement of VMs between datastore and in case where datastore are from different tires of Storage Systems, this can also be used as a Virtual Storage Tiering.

Benefits of Storage Tiering

  • Maximize Storage Efficiency at Lower Cost
  • Simplified administration
  • Decrease Drive Counts on the Array
  • Cost Reduction
  • Improve performance with wide striping on larger Storage Pools

Remember to understand your Storage array capabilities and understand its limitations before you implement.

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  1. February 28, 2013 at 11:00 pm

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