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Replaced bold [doesn't work in theme] with italics [hopefully works] for emphasis

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Joshua Boniface 2016-09-29 13:31:21 -04:00
parent 49ce41250b
commit 05642c5032
3 changed files with 9 additions and 9 deletions
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It is a common technique to provide **resiliency** and **availability** to a set of data and protect against one of the most common data loss scenarios: the failure of a disk.
It is a common technique to provide *resiliency* and *availability* to a set of data and protect against one of the most common data loss scenarios: the failure of a disk.
The simplest type of RAID is a 'mirror', which does just what it sounds like: keeps two (or more) copies of data on two (or more) different disks. If one disk fails, the second copy is still available and no data loss has occurred.

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Having a number of disks in RAID may **seem** like a backup, especially if you're using a mirror mode. But this is **wrong**!
Having a number of disks in RAID may *seem* like a backup, especially if you're using a mirror mode. But this is *wrong*!
RAID protects you against one and only one thing: a disk failure.
It does **not** protect you against any of the following things:
It does *not* protect you against any of the following things:
* Multiple disk failures beyond the RAID level chosen (e.g. both disks in a mirror, or 3 disks in a RAID-6).
* Failure of the RAID controller itself (especially when using hardware RAID), the computer running the RAID, or the environment (a flood, fire, theft, etc.).
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Even ZFS, designed specifically to prevent the third point, is still susceptable to the others.
The adage is simple: "RAID replicates **everything**, instantly, even the stuff you don't want." Like the deletion of a file or corruption.
The adage is simple: "RAID replicates *everything*, instantly, even the stuff you don't want." Like the deletion of a file or corruption.
For these reasons and more, RAID IS NOT A BACKUP!

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* Always back up in **some way**. While a copy of the data on the same array won't protect you against all problems, it will protect you against some.
* A **backup on the same server** is susceptable to the **same failures as the original data** set (hardware failure, natural disasters, and the like).
* A good rule of thumb is **three copies** (the RAID is only one copy for this purpose): the **original**, one **onsite copy**, and one **offsite copy**. Store the offsite copy in the cloud, or at a friend's house.
* **Make backups regularly**, at least once a week; the day you need a backup is the day you realize you hadn't run it in 6 months and what you need isn't backed up.
* **Test backups regularly**, at least once a month; **a backup is worthless if you can't restore from it**. Just because you have a backup doesn't mean you're protected; always test them.
* Always back up in *some way*. While a copy of the data on the same array won't protect you against all problems, it will protect you against some.
* A *backup on the same server* is susceptable to the *same failures as the original data* set (hardware failure, natural disasters, and the like).
* A good rule of thumb is *three copies* (the RAID is only one copy for this purpose): the *original*, one *onsite copy*, and one *offsite copy*. Store the offsite copy in the cloud, or at a friend's house.
* *Make backups regularly*, at least once a week; the day you need a backup is the day you realize you hadn't run it in 6 months and what you need isn't backed up.
* *Test backups regularly*, at least once a month; *a backup is worthless if you can't restore from it*. Just because you have a backup doesn't mean you're protected; always test them.
There are dozens of backup utilities out there; I'm not going to prosthelytize for any one of them, but I personally use [BackupPC](http://backuppc.sourceforge.net/) for my server and workstation backups.