Showing posts from July, 2020

Why every Spectrum Virtualize system should be using NPIV

The IBM Spectrum Virtualize software stack operates in clusters which are based on the Paxos Protocol
Therefore, in order to service a host's I/O request, each node must have the current cluster state information. When a node comes back online from a code upgrade (or reboot) it must pull this information from the running cluster. To be able to pull this data, the node must connect to the network so that the data can be transferred. This requires the node to bring its network interfaces online and log into the Fibre Channel (FC) network.
Naturally, the consequence of this is the propagation of RSCN (State Change Notifications) which then notifies all the hosts that the ports are back online (prompting login). However, the node will not be able to service SCSI I/O until the current cluster state is obtained from the other SV nodes in the cluster. Since the FC host logins are happening in parallel with the inter-node data transfer,  there is no way that the Spectrum Virtu…

Sizing the inter-site link for replication and multi-site environments

Hello friends. I've done a poor job this year of posting content regularly but hope this one helps make up for it. One of the frequently asked questions I get from administrators, technical sellers, and other engineers is how much bandwidth is required to perform replication or to sustain a multi-site environment. For the purposes of this conversation I am going to assume the use of Fibre Channel for the network.
The first part of this answer is very easy. Synchronous replication (and synchronous data patterns in the case of Global Mirror) require enough bandwidth to move the peak write throughput of the production workloads. If your peak write rate is 3Gigabytes per second (GB/s) then the math works out as:
3GByte           8bits ----------   X        -------    = 24Gbps, 2X16Gbps links or 3X8Gbps links 1s                    1Byte
For each Gbps on a standard port you can only achieve effectively 100MB/s as the standard interface is only capable of about 80% link efficiency on average.…