(SOLVED)can i recover data in a 1 parity -1 data disk server ?

[morty]

Hi

i have  2 disks of 6tb and want to use them to backup my data with redundancy,

i've readed that using 1 parity disk will suffice to recover from one data disk failure but

im not sure if this applies if there is only 2 disks (one working as parity the other as the only data disk)

 

will this setup protect me from the failure of any of the disks ? or is it necesary to have at least 2 data disks and one parity ?

 

or what would be the best setup to protect me from the failure of one of the disks ?

 

 

 

 

 

Edited June 5, 2021 by morty

[Squid]

A single disk as parity will be able to recover (in conjunction with every other working drive) a single data disk failure, regardless if you have 1 data drive or 24.

 

A dual disk parity will do the same for 2 data disk failures.

 

Upshot of how Unraid handles things vs pretty much every other solution out there is that if 2 or more drives happen to die at the same time, then you will only ever lose a portion of your data, not everything (every other company in the world seems to think that you're better off if you exceed your redundancy that you're better off losing every single movie, television show, baby picture rather than (Limetech's philosophy) only losing a couple movies, television shows, or the baby pictures that didn't turn out quite right)

[itimpi]

No - 1 data + 1 parity is fine.

 

in fact it turns out to be a special case as the result of the parity calculation means that the parity disk is identical to the data disk right down to the bit level.    This is not true when you have more than 1 data disk.

[morty]

awesome , thank you for the info i will go ahead and setup one parity and one data,

 

yes i agree, i choosed unraid over other home solutions because i prefer to lose partial data probably "homework folder"

over losing everything ..

 

@itimpi i saw the spaceinvader one explanation, so yea that was part of the reason i was wondering if it will work

 

 

[6of6]

I would use one disk for data and the other for backup (no parity). Maybe I missed something?

 

6.

[morty]

On 5/19/2021 at 11:58 PM, 6of6 said:

I would use one disk for data and the other for backup (no parity). Maybe I missed something?

 

6.

that would be also interesting but how would you sync the two disks constantly ?

[6of6]

Constantly?... Maybe that's what I was missing...

 

If I had only two (2) drives, I would use one for data and the other for backup. I wouldn't try to clone/sync one to the other, but think about what's important on the data disk (maybe stuff after downloading/processing) and only backup the stuff that is really important.

 

At my skill level, on unraid, I would use LuckyBackup (as I do). It uses rsync that can backup/synchronize drives beyond my skill level.

 

I guess my main idea is that I would choose backup over parity.

 

I hope this helps.

 

6.

[JonathanM]

5 hours ago, morty said:

that would be also interesting but how would you sync the two disks constantly ?

If you sync everything, that's not a good backup, as deletions and corruptions are instantly updated. Backup implies being able to retrieve previous versions of files.

[morty]

15 hours ago, 6of6 said:

Constantly?... Maybe that's what I was missing...

 

If I had only two (2) drives, I would use one for data and the other for backup. I wouldn't try to clone/sync one to the other, but think about what's important on the data disk (maybe stuff after downloading/processing) and only backup the stuff that is really important.

 

At my skill level, on unraid, I would use LuckyBackup (as I do). It uses rsync that can backup/synchronize drives beyond my skill level.

 

I guess my main idea is that I would choose backup over parity.

 

I hope this helps.

 

6.

 i apreciate you shared your method, i will look into LuckyBackup,

the way i copy my files is using cygwin with rsync , using a bash script with a list of directories to be sent to unraid,

once a month i just run the script and all the new/modified files are sent to unraid ,

also have a docker gitea in unraid to keep projects versioning

 

so i just let the unraid parity process to execute once a month and that way i spect to have redundancy of the files in my two unraid disks,

so its mostly an automated process

 

if i get a disk failure on my unraid box i hope i will be able to recover all the data either from the parity or from the data disk

and in the future feel free to delete files from my windows box knowing there is a safe copy on unraid

 

 

11 hours ago, jonathanm said:

If you sync everything, that's not a good backup, as deletions and corruptions are instantly updated. Backup implies being able to retrieve previous versions of files.

 

yes im not saving files history , i use the unraid box to store personal files from my main windows pc (with the risk you mention of corrupted files)

thank you for pointing that out

 

 

[JonathanM]

5 hours ago, morty said:

feel free to delete files from my windows box knowing there is a safe copy on unraid

If it's the only copy, it's not safe. You still need backup. Unraid can protect from outright disk failure, but that's only 1 of many ways to lose data.

[6of6]

On 6/5/2021 at 3:43 PM, morty said:

i spect to have redundancy

To me, parity/redundancy is just a way to keep things running. I want my server to run 24/7/365 (366 on leap years). If ( when :(  drives fail... I hope/expect unraid to make it easier to keep things running. Less down time, rebuild, etc...

 

My backup is my *guarantee* that everything will, eventually, work again... period!

 

6.