Sunday, January 11, 2015

Software-Defined SANs

The headline caught my attention - Server SANs: Don't throw the baby out with the bathwater

The author does a really good job of discussing the advantages and disadvantages of leveraging server storage as a virtual Storage Area Network (SAN).

I'm sure that the bean counters will jump on this and that the server salesmen will push this because it will help them sell more kit.

But this is really a bad idea.

While the following example is regarding ancient technology, the math doesn't change.

IBM 3380 Standard DASD had issues with internal paths. The details are arcane and not directly applicable to this discussion but suffice it to say that as you increased the capacity of the 3380 sub-system, the performance degraded. Worse the performance was different to different devices. While the average degraded gracefully, the standard deviation was all over the place. Siebo Friesenborg and I had a spirited discussion of this at the IBM Washington Systems Center.

The result was that the performance was erratic and very hard to manage.

Mapping the local storage of a cluster of servers into a virtual SAN can't help but suffer the same characteristics.

Storage that is mapped locally on a server will undoubtedly perform better than storage that is mapped 2 servers away.

Complicate the locality issue with the all too frequent I/O bandwidth issues of blade servers and you've got a solution that will make the performance consultants happy.

Call me.

No comments: