A question that often comes up from customers is “How does the tiering in Spectrum Control differ from what is available in EasyTier as part of SVC/Storwize?” This is a valid question which merits a detailed answer. Before getting into the specifics of EasyTier let us get some terminology out of the way. We all agree that IBM SAN Volume Controller (SVC) or Storwize will act as a storage hypervisor and will allow you to virtualize your existing legacy storage whether it be from EMC or HDS or Oracle.
In the above diagram, legacy EMC or HDS storage shown as DISK Subsystem will have disks (spinning HDD and NAND flash based SSD) and RAID controllers, the disk subsystem exposes SCSI LUNs to IBM SVC. SVC views the world in terms of managed disks (mdisk) and groups of mdisks constitute a storage pool. These mdisks in turn can be divided into “extents” and these extents can be combined to create virtual volumes which are each assigned a logical unit number (LUN). Your host application whether it be DB2 or Oracle or SAP sees only these virtual volumes exposed by IBM SVC – it doesn’t know nor should it care about the internal workings of SVC.
As a storage administrator you decide to derive the benefits of EasyTier. You may choose to create a “multi-tier storage pool” comprising HDD mdisks and SSD mdisks and enable EasyTier on it. EasyTier will monitor the I/O and latency on back-end extents of all volumes within this pool. It will dynamically migrate “hot” extents to a faster disk tier within the pool, “cold” extents will be moved from faster tier mdisks to slower tier mdisks. In other words EasyTier is doing sub-LUN level optimization within the boundaries of a storage pool for workloads that are not cache-friendly.
Spectrum Control adds further value to EasyTier in the following ways:
- Enabling optimization of entire volumes across the boundaries of storage pools giving you the added flexibility to migrate a “hot volume” across storage pools
- Balancing workloads across multiple pools to help you avoid hotspots and bottlenecks
- Take corrective action in case of overloaded pools (pools which say may not have enough SSD capacity in a pool configuration)
- Providing visibility into the type of disks (near-line, SAS, SSD) that constitute the storage pool and helps you understand how volumes are residing within different disk tiers.
If you have Spectrum Control in-house try this all out for yourself, if you don’t and want to experiment with the SaaS equivalent namely Spectrum Control Storage Insights check out the blog post from my colleague Jenny Shaw. With a newly introduced entry price of $250 dollars per month for the first 50 terabytes of usable storage, you can’t go wrong giving Spectrum Control Storage Insights a test drive.