I’ve just been speaking with one of our storage sellers on the subject of immutability (Cyber Resiliency is the new black, dontchaknow?), the subject of “nearline” came up and they couldn’t understand why this may help or even differentiate from normal disk storage. After talking around the subject, it turned out that the seller was primarily a block storage sales person and we were talking about tape.
So what’s the difference?
“Nearline” when talking about removable media is a term to differentiate media which are stored offline but can be brought back online automatically. The most common technology to do this would be a tape library, where robotics move a piece of media from a shelf to a drive. Optical disk autoloaders would also be a nearline technology.
“Offline” when talking about removable media requires human interaction to bring the media online, this would be tape on a shelf, optical platter, disk cartridge or even your CDs/Vinyl (I may be showing may age with that last one…)
Now, when we’re talking about disk technologies “Nearline” is almost totally different. A Nearline SAS disk AKA “NL-SAS” is essentially mechanically SATA hardware with a controller that presents as SAS. They are less performant than SAS disks and also SSD/Flash storage but more dense, so individual disks come in larger sizes. These disks are, however, more performant than traditional SATA equivalent and an existing array can accept them without modification.
It seems that the use of the name “Nearline” for these disks comes to distinguish them from the traditional primary, high performance online storage tier.
It is important to make sure that anyone you’re speaking to on the subject of Cyber Resiliency, Immutability and more general data protection, fully understand what’s being spoken about when we talk about Nearline. Many companies have good cause to muddy the waters when comparing these technologies, what with having poor-to-no truly nearline or offline storage options.