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Server

Do mounted folders get mirrored with RAID1?

stackQA

8/3/24, 9:31 AM

I have two drives configured for RAID1 on a a centos 7.9 server. I have been running out of space, installed a third drive and relocated the /opt folder to this third drive.

I still seem to be running out of disk space.

With these two drives in a RAID1 configuration, and those drives mount a third drive, are the contents of this third drive included in the RAID1 mirror?

If so this would seem odd to me, as I do not want to have USB data backed up every time I mount it.

2 + 1

raid1

Nikita Kipriyanov

8/3/24, 4:05 PM

Honestly, this was a bad idea to move something to non-mirrored drive, if it's needed for the system to perform its task, especially USB drive (because USB has high latency — USB mass storage is *very slow*). This defeats the purpose of having RAID1. If you are running out of space, consider investigating **what** consumes all the space and **why** and solve that problem instead.

Score:3

Server

Zac67

8/3/24, 10:55 AM

RAID1 is no backup. It's mirroring to improve availability. You still need to back up your data on a regular basis.

If you add a third drive, then you logically have two drives: the previous logical drive, backed by RAID1, and the new one. Mounting a volume just creates a reference, so both drives (or rather volumes) still stay separate on the file system level.

If you regularly back up your RAID1 volume, you need to check whether that job automatically includes your new drive. That depends on how the backup is set up and there's no standard rule.

+ 1

stackQA

8/3/24, 11:58 AM

Thanks @Zac67. I have edited the question title with the correct terminology. I don't have a backup mechanism setup like rsync or borgbackup. That is something else I need to do.

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Server

Nikita Kipriyanov

8/3/24, 3:53 PM

This totally depends on the backup solution you use:

Proxmox Backup doesn't span file systems by itself, so if you point it to some directory in a parent system, it won't include contents of mountpoints, so if you need their contents, you must specify them individually.
Veeam also requires you to specify all the mounted file systems individually, else it "does not guarantee that OS will boot" (as if people use it specifically to backup OS for bare metal recovery, and not for data backups. It has the worst explanation of all).
BareOS includes contents of mounted file systems into backup by default, but you can configure it to not to include by setting OneFS=no in the corresponding FileSet resource.
tar has an option --one-file-system which tells it not to descend into directory if it's a mountpoint, but by default it will. As Amanda uses tar to backup directories, it should inherit this behaviour. In other words, it behaves like BareOS.

and so on. I am not able to list them all; there are zillion of different backup solutions. You need to read manuals of your backup software carefully, and do your own tests if this is still not clear.

+ 5

stackQA

8/5/24, 4:41 AM

Thanks for the answer @Nikita. Some very good info which I appreciate. However I don't have a backup mechanism ... yet. Essentially I took the tools folder and placed in on a newly installed drive. The tools can be reproduced with an installation. The server is in a data centre. Again, thanks for the info. Much appreciated

djdomi

8/6/24, 5:58 AM

veeam backup the data that has been configured. not more and not less. if you backup an entire machine then it is possible, if you backup only it's data... you know the way I mean ;)

Nikita Kipriyanov

8/6/24, 10:21 AM

@djdcomi I have `/dev/mapper/vg0-lv0` mounted to `/var/lib/mysql` and configured Veeam to backup `/var`, should I expect it to back up my volume with databases too? Does it think I configured this data to be backed up or not? Different solutions have **different answers** to this question and have **documented it**, of all Veeam's documentation has the most vague answer. This is the whole point of the answer.

djdomi

8/7/24, 3:58 PM

the best way is just to open a case on veeam, and ask them for the best practice imho

Nikita Kipriyanov

8/7/24, 4:50 PM

Why would I worry? Let Veeam users worry. Hopefully, they won't face the reality the hard way. Everybody else was able to clearly document this caveat, except Veeam, I have a plenty of decent backup systems to choose.

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