raidz2 math

[rcrh]

So I've created a raidz2 volume with seven 2tb drives. I was expecting to have 10tb of storage available after two of the drives were used for parity. But, Freenas is reporting only 8.3tb available. Is this marketing "rounding" caused because a 2tb drive is really only 1.8tb? Or, did I do something wrong?

 

[cyberjock]

My guess is rounding.

If you had accidentally chosen 6 drives you'd have 8TB total(minus some for marketing "rounding").

I'd say if you are sure your configuration is RAIDZ2 then all is well. I say this only because you are questioning your configuration and if you had chosen 6 drives on a RAIDZ1 you'd have the exact same amount of space free.

 

[ProtoSD]

You'll get better performance with either 6 or 8 disks and RAIDz2. Even numbers of disks for RAIDz2 (4,6,8), odd numbers for RAIDz1 (3,5,7).

 

[rcrh]

Nope. Definitely seven drives in the case and all are in the one volume.

Thanks for the succession.

 

[rcrh]

You'll get better performance with either 6 or 8 disks and RAIDz2. Even numbers of disks for RAIDz2 (4,6,8), odd numbers for RAIDz1 (3,5,7).

Shoot. I forgot about that guidance. I tell ya, the small amount of data I've moved to the volume so far has been incredibly slow. I may pull the plug and rebuild it with size discs.

Thanks.

 

[gpsguy]

At the end of the day, your 3.5Gb? of RAM, is a contributing factor to your performance issue.

I tell ya, the small amount of data I've moved to the volume so far has been incredibly slow. I may pull the plug and rebuild it with size discs.

How are you transferring the data? If CIFS - read the various threads about it. On my Gb LAN, using FTP is about twice as fast as CIFS.

 

[StephenFry]

I may pull the plug and rebuild it with size discs.

It's what I did; go for six (or if you're brave, ten) disks. Eight isn't ideal either.
Performance will be excellent with both 6 or 10 - mine is so fast now that either the Gbit line or source HDD are the bottleneck. And yes, that's using CIFS.