Dual Parity Question

[fonzie]

My current setup:

 

Parity

1x 5TB Drive

 

Data

6x 2TB Drives

4x 4TB Drives

 

As you can see, my largest data drives are only 4TB.  My questions is: can I add a second parity drive that is only 4TB in size if I do NOT plan on adding any data drives past that number?  If yes, will I have that double parity protection with that second drive installed?

 

There are not many 5TB drives to choose from (not a popular size) and the 6TB jump isn't worth it for me right now.

[JorgeB]

Yes and yes.

[fonzie]

Great to hear, thanks!

[fonzie]

follow up question:

 

Does dual parity protect you from two data disk drives failing?  Or does it only protect one data and one parity drive failing simultaneously?

[Squid]

Dual parity means that any two drives can be recovered should they die (except for the cache)

 

Sent from my LG-D852 using Tapatalk

 

 

[fonzie]

Interesting.  I understand how single drive parity works with the bits being calculated and matched up.  Does anyone have a link to an explanation as to how the dual parity works?

[trurl]

Interesting.  I understand how single drive parity works with the bits being calculated and matched up.  Does anyone have a link to an explanation as to how the dual parity works?

See this limetech post for a link.

[fonzie]

Thanks for the link.  So dual parity works in the same way that RAID6 works, it seems.

 

Looks way more complicated than single drive parity. 

[garycase]

Thanks for the link.  So dual parity works in the same way that RAID6 works, it seems.

 

Looks way more complicated than single drive parity.

 

It's not the same as RAID-6, but it certainly has the same effective fault tolerance ... i.e. it can tolerate any two drive failures with no loss of data.    And yes, the 2nd parity calculation is a good bit more complex than the first parity, which is a simply longitudinal XOR parity calculation.

 

[John_M]

The algorithm is the same (and can make use of processor optimisations aimed at improving RAID6 performance), though RAID6's striping of data and parity is not used.

[testdasi]

One thing I recommend is to check the exact size of your 4TB in bytes to be sure. For some reasons, 4TB discs have slightly different exact size depending on brand / model. Last thing you want is to clear out 1 disc and then realise it's a few MB smaller than another 4TB.

[trurl]

One thing I recommend is to check the exact size of your 4TB in bytes to be sure. For some reasons, 4TB discs have slightly different exact size depending on brand / model. Last thing you want is to clear out 1 disc and then realise it's a few MB smaller than another 4TB.

It has nothing to do with brand / model, and the reason is well known. Something has put a HPA (Host Protected Area) on the disk. This has been discussed on many, many threads on the forum. A search of the forum for HPA turns up 33 pages of matches. See How to Search sticky linked in my sig.

 

*edit*

 

Also, HPAs can be removed before you put any data on the disk. Drive manufacturers have to have standards about disk sizes since traditional RAID requires disks to be the same size.

[testdasi]

I thought it was due to HPA originally too but I bought 2 4TB in the past, a WD Red and the Hitachi still in my sig and the size were slightly different. Double checked that it wasn't due to HPA too. The WD Red ended up dead eventually so maybe it was wonkie off the bat but for sure not HPA related.

[gubbgnutten]

I thought it was due to HPA originally too but I bought 2 4TB in the past, a WD Red and the Hitachi still in my sig and the size were slightly different. Double checked that it wasn't due to HPA too. The WD Red ended up dead eventually so maybe it was wonkie off the bat but for sure not HPA related.

 

Did you check the serial number of the red? Some sellers have harvested drives from external mybook drives and sold them as reds... Some users have had problems with such harvested drives being smaller.