Brand new 18TB Pegasus2 R6 Thunderbolt 2 RAID only showing 15TB - missing 3TB

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  • Last Post 08 January 2017
Brian Caine posted this 08 January 2017

I got a Brand new 18TB Pegasus2 R6 Thunderbolt 2 RAID 2 days ago that I have connected to an iMac.

The Pegasus is showing a storage capacity of 15TB but if I look at it in the Promise Utility, it shows there is 18TB configured as it should be.

Sorry for this clearly newbie question, but How does one go about verifying all the drives or seeing if I need to wake up the 6th drive with the addition 3TB.

Thanks

 

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Richard Oettinger posted this 08 January 2017

RAID5 means that every chunk of data that your Mac writes to the Pegasus volume will be divided in to five pieces - with each piece going to one of the drives in the Logical Drive - and then a "parity" calculation is performed on that chunk, with the result going to the sixth drive.

so in effect you really are using all the capacity, it's just that you have 15TB for your actual data as 3TB will be consumed by the parity data.

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Brian Caine posted this 08 January 2017

Thank you Richard for the very quick response - so if I understand correctly, even though you have an 18TB drive capacity, 3TB is really there just to back up in the event one of the other drives fails ...

... so in actuality the storage capacity is 15 TB.

Still learning the terminology, but yes, I am seeing in the utility that the Logical Drive capacity is 15 TB and the RAID Level is at RAID5.  So, you would be correct.

Thanks.

 

 

Richard Oettinger posted this 08 January 2017

Hi Brian,

the most likely reason is that there is a RAID5 Logical Drive on your Pegasus. This RAID level means the capacity of one drive will be consumed for the parity structure that protects your data against a drive failure.

you can verify that in the Utility.

cheers

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