DSM-G600, DNS-3xx and NSA-220 Hack Forum

Thanks for the reply, fordem.

My understanding of the RAID features was to either have a 2nd drive act as an expansion to the 1st one, or to have the 2nd drive mirror/clone the 1st one.  I've never used RAID before so if I need correcting please do so

So has anyone used a USB hub to expand the USB host?

Thanks!!

There are different types or levels of RAID - this device supports two - RAID0 & RAID1

RAID0 "stripes" the data across both disks - it writes a chunk of data to disk0 and then a chunk to disk1, and then writes to disk0 and then disk1 and so on - the idea here it to extract as much speed as possible, this works well when the disk and it's interface is the bottleneck that causes the slow down - BUT - that is not the case with the DNS-323 and you will find if you test that there is no performance advantage to RAID0.

With RAID0, if either disks fails you WILL lose ALL the data stored

RAID1 "mirrors" the disks - whatever data is written to disk0 is also written to disk1, the idea being that if a disk fails the data remains available from the second disk.  Many people mistakenly feel that RAID1 can be considered a form of backup (hence my warning) - if a file is deleted either deliberately or accidentally, it's deleted - same thing goes if it's corrupted by a virus, it's gone.

With RAID1 you lose 50% of the available drive capacity - there is a theoretical performace improvement when reading as both disks can be read, but as with RAID1 this is not realised with the DNS-323

Neither form of RAID supported on the device allows the second drive to act as an expansion of the first, although with RAID0, the two disks shows a single disk, which I suppose could be considered an expansion, there is however an additional format option called JBOD - or Just a Bunch of Disks - which also creates a single volume.

With JBOD (on a DNS-323) data is written to the first disk and when that is filled any additional data goes to the second disk - this is different to RAID0 where data is written to both disks all of the time - but - like RAID0, failure of either disk results in loss of all data (even if all of the data is stored on one disk)

The generally accepted position on this forum seems to be that the best usage of the device is with each disk separate and run somesort of backup from one disk to the other.

Thanks a lot for all these replies, its really answered everything I wanted to know about the device and much appreciated.

Now I can see why RAID1 is confused as a backup but like you suggested, fordem, might be best to have drives running independently - thanks for explaining how it all works.

I'm so glad to hear USB hub as a possibilty!