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Fixed markdown formatting

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Joshua Boniface 2016-09-28 12:25:10 -04:00
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commit 112e622367
4 changed files with 11 additions and 11 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. 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: RAID protects you against one and only one thing: a disk failure. It does **not** protect you against any of the following things:
1. Multiple disk failures beyond the RAID level chosen (e.g. both disks in a mirror, or 3 disks in a RAID-6). 1. Multiple disk failures beyond the RAID level chosen (e.g. both disks in a mirror, or 3 disks in a RAID-6).
2. Failure of the RAID controller itself (especially when using hardware RAID), the computer itself, or the environment (a flood, or fire, perhaps). 2. Failure of the RAID controller itself (especially when using hardware RAID), the computer itself, or the environment (a flood, or fire, perhaps).
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4. File corruption from bad writes or bit rot (except for ZFS), including whole-volume corruption from administrative mistakes (e.g. =mkfs= on an existing filesystem). 4. File corruption from bad writes or bit rot (except for ZFS), including whole-volume corruption from administrative mistakes (e.g. =mkfs= on an existing filesystem).
5. Malicious or accidental deletion or modification of data by yourself or another party, including viruses. 5. Malicious or accidental deletion or modification of data by yourself or another party, including viruses.
The adage is simple: "RAID replicates _everything_, even the stuff you don't want, like the deletion of that file you needed." The adage is simple: "RAID replicates **everything**, even the stuff you don't want, like the deletion of that file you needed."
For these reasons and more, RAID IS NOT A BACKUP! For these reasons and more, RAID IS NOT A BACKUP!

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1. 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. * 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.
2. 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 **backup on the same server** is susceptable to the **same failures as the original data** set (hardware failure, natural disasters, and the like).
3. 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. * 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.
4. _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. * **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.
5. _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. * **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. 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.

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More information can be found on the following pages: More information can be found on the following pages:
http://blog.open-e.com/why-raid-is-not-a-backup/ * http://blog.open-e.com/why-raid-is-not-a-backup/
http://serverfault.com/questions/2888/why-is-raid-not-a-backup * http://serverfault.com/questions/2888/why-is-raid-not-a-backup