Inside Storage Networking

I frequently work cases where the problem is a performance problem.  Either an entire system or an application is slow enough that users are affected.    Another frequent performance problem is with storage-side replication.  In these cases replication is not able to keep up with the production workload and RPOs are not being met.   Replication is done most commonly between sites, though I have worked a few cases with same-site (or campus) replication.     Whether you are using IBM DS8000 PPRC/Global Mirror, IBM SVC/FlashSystem Global Mirror (GM) or Global Mirror with Change Volumes (GMCV) you expect that the replicated data will be current up to a certain point in time behind the production data.  This is your Recovery Point Objective (RPO).    Your RPO is how current the replicated data needs to be.  For data that doesn't change often, an RPO of 30 minutes or an hour might be enough.  For data that frequently change...

  I recently posted  this post  on how you can help IBM Storage Support help you by ensuring you are utilizing the full monitoring features available on your storage systems and switches.    You should also have at least the free version of IBM Storage Insights installed.   If you have Storage Insights Pro or Storage Insights for Spectrum control, there are some additional steps that you should take that will benefit both you and the IBM Support team resolve your problems as quickly as possible.  IBM Storage Insights Pro and Storage Insights for Spectrum Control come with some powerful features for grouping and  organizing storage resources.  These features are found under the Groups menu.   You can organize your storage resources into Applications, Departments and General Groups.    There is a hierarchy to the organization of resources.   Departments can contain sub-departments, Applications or General Grou...

Why Low I/O Rates Can Result in High Response Times for Reads and Writes As IBM Storage Insights and Storage Insights Pro become more widely adopted, many companies who weren't doing performance monitoring previously are now able to see the performance of their managed storage systems. With the Alerting features on Storage Insights Pro, companies are much more aware of performance problems within their storage networks. One common question that comes up is why a volume with low I/O rates can have very high response times. Often these high response times are present even with no obvious performance impact at the application layer. These response time spikes generally measured in the 10s or 100s of milliseconds, but can be a second or greater. At the same time, the I/O rates are low - perhaps 10 I/Os per second or less. This can occur on either read or write I/Os. As an example, this picture shows a typical pattern of generally low I/O rates with a high response time. The volume...