Total Volume not being displayed in ReadyNas104

Thanks also for all your replies and helping me understand a little more! More than that of the person who sold me the Nas who said it was a case of pugging it in and transfer data! and also that of the Netgear telephone support that couldn't understand my basic requirements of setting up a Nas!

Thanks again!

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DanEv wrote:

Sorry just when I think I understand how it works I find more questions! So If I had a total of 1200Gb of Data on my Nas it allocates 6000Gb for Protection does this mean I have 6000Gb of unprotected data or is protected data compressed?

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I think you must have meant 12000GB of data???

With RAID-5,  all the data is protected from a single disk failure, and there is no compression.  It is a bit hard to explain though.

The data is organized in blocks.  If you had 3x6TB drives (for example) then for every 2 data blocks there is also one parity block.  All three blocks would be on different disks.  You can think of this as setting up an equation:

DataBlock1 + DataBlock2 = ParityBlock

If the disk with DataBlock2 fails, then the system rebuilds it, by solving the equation:

DataBlock2 = ParityBlock - DataBlock1

If you had 6x3TB, then for every 5 datablocks there is also one parity block,and again all are placed on different disks.

DataBlock1 + DataBlock2 + DataBlock3 + DataBlock4 + DataBlock5 = ParityBlock.

Recovery works the same way as the 3x6TB example.  The contents of any missing disk can be reconstructed from the remaining disks by solving the relevant equation for each block.  So if one of the other blocks in the group can't be read, then you are out of luck.  That can/does happen, and is why we recommend backups (and not relying just on RAID).

BTW RAID doesn't actually use normal addition in the equations -  it uses XOR instead.