Snapshot 101: Copy-on-write vs Redirect-on-write

Good post by W. Curtis Preston (thank you)

There are two very different ways to create snapshots: copy-on-write and redirect-on-write. If IT is considering using the snapshot functionality of their storage system, it is essential to understand which type of snapshot it creates and the pros and cons of using either method.

Rather than the more common term volume, this column will use the term protected entity to refer to the entity being protected by a given snapshot. While it is true that the protected entity is typically a RAID volume, it is also true that some object storage systems do not use RAID. Their snapshots may be designed to protect other entities, including containers, a NAS share, etc. In this case, the protected entity may reside on a number of disk drives, but it does not reside on a volume in the RAID or LUN sense.

Read on here

Stick a Needle in Your IOPS

Good Post by vMiss (thank you)

What are IOPS anyway?  Simply put, they are Input/Output Operations Per Second, and they are meaningless.

Wait, what?  How could I possibly be calling IOPS meaningless?  I’m a STORAGE person!  How could I say this? I think that maybe it was one of those metrics that had meaning, at one point.  Maybe.  Now?  Not so much.  Here’s why.

Let’s say I go down to the Storage Depot and I’m looking at all the shiny storage controllers on the shelves.  I point at the prettiest one, and I ask the helpful person with the name tag how many IOPS I can get out of it.

Read on here