Raid0 in a Raid1?

[reclinarka]

Hi guys,

I wanted to ask if anyone knows if it's possible to have three HDD's where two of them are in a Raid0 while this Raid0 is in a Raid1 with the third HDD.

Sorry if it's a stupid question but I didn't find a answer to it so far.

Thanks for any answers!

Kind regards

Phil

[zMeul]

it's called RAID5, but the controller has to know it - it works with at least 3 drives

you can also use RAID4, but the write performance is lower

[reclinarka]

Thank you for the fast reply but is there a way where I can use the full speed of the raid0 and use the third HDD more like an automated backup?

[zMeul]

Thank you for the fast reply but is there a way where I can use the full speed of the raid0 and use the third HDD more like an automated backup?

not really, your best performer will be RAID5 with the parity distributed on all 3 drives - one can fail

the RAID4 has a dedicated parity drive - one can fail; but as I said, because the parity is written to a single drive, the overall write performance takes a penalty hit

 

and PS: RAID is not backup !!!

[Tagiau]

Just buy a fourth drive and put everything in raid 10. I wouldn't deal with raid 5 as if one thing messes up it is very likely to take everything with it.

[reclinarka]

Do you think it's worth giving up storage and instead just use a RAID1 between SSD's? I wan't to use it for video editing and to prevent the frustration of data loss after editing without the loss of speed.

[BiggHertz]

Hi There,

 

You state that you would like to use this volume for video editing. That type of I/0 can vary between sequential and random read/writes. Any RAID that requires a parity calculation(s) to be performed is NOT ideal for this type of I/O workload as this calculation requires overhead. Some dedicated hardware RAID controllers have on-board cache(backed with a battery backup) to help buffer the incoming flow of data. Some software/hardware RAID can utilize an SSD as cache to use a buffer until it can be written to the array, this is not as fast as the memory based cached found on most HW RAID controllers.

 

Typically a video editing workflow would consist of a scratch volume, where actively edited video content is housed. These are typically a very fast SSD or an array of SSDs/HDDs. Once work is at a save point, you can copy to more redundant storage solution. If the scratch disk crashes, data can be recalled from this redundant storage.

 

A good compromise for performance would a RAID (1+0) commonly referred to as RAID 10. This minimally requires 4 drives, which are arranged as mirrored sets with striping between them. Storage capacity is reduced in half, but write/read speed typically(RAID Controllers do not all scale performance in the same matter) increase as the number of stripped sets increases(Parallel Streams of Data from each set). With regards to redundancy, in the 4 disk example, two drives can indeed fail as long as the failures are limited to 1 disk per mirrored set.

 

Hope that helps.

 

-Jason

[zMeul]

two drives can indeed fail as long as the failures are limited to 1 disk per mirrored set.

not entirely true,

recoverable fails with 2 drives:

x o | o x | x x | o o

o x | x o | o o | x x

unrecoverable fails:

x o | o x

x o | o x

array as follows:

1 1

2 2

[BiggHertz]

You're referencing a 0+1, the example I provided was 1+0 commonly referred as RAID 10.