pool or array?

[userano218n]

I am now running with a 4 disk zfs pool.  the array seems required, so i just plugged in a 128mb usb drive and it seemed happy and lets me start the array which brings my pool online.  what are the use cases for why i would need an array vs a pool?  im trying to understand the differences between the two and why the array is required.

 

thanks!

[Gragorg]

The requirement for an array device is going to be removed in a future release.  The ZFS zpool has higher performance but drives do not spin down.  The array allows you mix and match hard drive sizes and expand one drive at a time when needed.  It also spins down unused drives to save power but performance is limited to the performance of a single drive as data is not striped.  If you lose one drive your data is covered in both cases (array and raidz).  If you lose two drives the raidz pool you would lose your data while the array would only lose the two failed disks and all remaining data would be intact.  You can add a second parity to the array to have a two disk fault tolerance. 

[userano218n]

Would the 2nd parity be the same as doing raidz2?

Edited April 7 by userano218n

[itimpi]

21 minutes ago, userano218n said:

Would the 2nd parity be the same as doing raidz2?

 

Not really as the Unraid approach to parity is very different to a traditional RAID system.   As an example the Unraid array has each disk as a separate file system (that can be read on another system by itself if needed), and you can use a mix of the supported file systems in the Unraid array.  It WOULD, however, allow for any 2 disks failing in the Unraid array and being able to recover their contents.