Overview, types of storage:

  1. Primary – RAM, volatile memory
    1. Instantaneous access time (in nanosecond area)
  2. Secondary – non-volatile, harddisks (magnetic/HDD), SSD, floppy disks, tape drives
    1. HDDs: access times of fast hard disks are typically from 5 to 10 milliseconds (pcmag)
    2. SSDs: access times are in the 25 to 100 microsecond range. SSDs are as much as 100 times faster (pcmag)
  3. Tertiary storage – a.k.a. nearline storage
  4. Off-line storage – optical discs, flash drives, …
Online / Production (1) Backup (2) Archive (3)
General description Instant use, continuously used, all the time the computer is on and in use Making copy of the current and active data in use, copy of Online (1) data on different medias and locations – do note plurals. Repositories for data that one wants to be kept for a long period of time but is not necessarily important for operational activities.
For Operating system, applications, and all your data (configurations, documents) Optimally, all data from Online (1) is saved onto some backup device(s) – i.e. including OS, apps, and all data. Important documents, emails, messages, photos, video, audio (multimedia), … but also – and DON’T forget this – *applications* and *hardware* that can read and work with archive media and data, over a long time (think decades for personal photo album).
Data size relation All Current “1:1” to “1/2:1” or “2:1” to All Current. I.e. all or some parts of Current is backed up (may exclude OS, apps) (represented by 1/2:1), or could be the reverse – Backup disk is larger than Prod, for multiple copies on same disk (like VMs and Snapshots). “N:1”, N being larger than 1, over time. I.e. over time, archived data will “always” be larger than Current.
  Example 1 TB disk 500 GB SSD ext. disk for backups of docs,
2 TB SSD ext disk for (e.g.) Time Machine
5 TB ext HDD disk, media, docs
2 TB cloud svc, media, docs
+ more HDD disks, cloud svcs
Characteristics * Speed, Reliability – more important
– Cost is less important
* Speed, Reliability – more important
– Cost is still less important
* Longevity – reliability over long time
Good solutions
  • HDD and SSD disks (always connected, part of computer/server/device – like smart phone, tablet)
  1. HDD and SSD disks (always connected)
  2. Cloud services (Dropbox, et c)
  1. Optical disks: *Archive*-style CDs/DVDs
  2. Tape (historically good tech)
  3. HDD drives, *NOT* any SSDs
  4. Cloud services (Dropbox …)



More technical, speeds, …