RAID1

[Totohenk]

Will I have 2TB space if I put 4 1TB HDDs in RAID1?

[Mark77]

Yes, assuming you configure them as mirroring each other.  You could also do a double or triple mirror.  A triple mirror of 4 1TB HDDs would yield 1TB of storage. 

[Totohenk]

So with double mirror 2TB space?

[Zyndo]

RAID 1 will give you no speed increase, and mirroring of your drives. so 4 1TB drives gives you 2 TB of storage, and 2 TB of mirrored storage.

 

I'm not sure how to go about setting it up, but with 4 1TB drives you may consider a RAID 0+1 setup (I believe this is the same as RAID 10). You still get 2 TB of storage and 2TB of mirrored storage,  but your 2 TB of storage operates like a RAID 0 stripped operation. So you will get a speed boost for that setup without sacrificing capacity.

[Mark77]

Actually a properly implemented RAID 1 will roughly double the read performance if 2 drives are mirrored.  Triple if three drives are mirrored.  Quadruple if four drives are mirrored.  Given appropriate workloads.  Write performance, unfortunately, will always be that of the single slowest drive as data must be written to each of the mirrors in its entirety.

 

RAID 10 is slightly different than RAID 0+1, in that, the host can do some optimization over which drives are dispatched to do the actual reads, and adjacent stripes do not necessarily have to be on the same disk.  So you can get quite a performance boost with an overall "RAID-10" implementation versus a striped mirrorset (ie: 0+1).

[Mark77]

"So with double mirror 2TB space? "

 

Nope, with a single mirror, 2TB (ie: 2 drives mirrored onto 2 other drives). 

 

With a double mirror (ie: 3 drives mirrored onto each other), you'll have 1Tb of redundant space, and 1 Tb of non-redundant capacity

 

With a triple mirror (ie: 4 drives mirrored onto each other), you'll have 1Tb of highly redundant space (ie: able to tolerate loss of 3 drives).  Seems quite overkill to me, but its certainly a possibility.

 

Usually most people just do the single mirror for RAID-1, but in high reliability or high read-intensive I/O scenarios, I've seen more done in an attempt to speed things up.

[Totohenk]

Thanks

I will run RAID1 in single mirror.

 

(Speed doesn't matter to me because it is for a archival NAS).