# How heavy is a useable Petabyte?

The team at MatrixStore have a post up calculating the weight of a petabyte of storage today compared to 1980.  Needless to say todays weight was a lot less.  The article was inspired by a post on Gizmodo illustrating how big a PB is.  There are two problems with the calculations though.

1. 2TB is a marketing number.  The formatted capacity of 500 2TB drives is more like 916TB
2. The weight is for the drives alone, which is not storage you could actually access and use

If we want to use 2TB drives we need a system that can hold 3.5″ drives.  The highest capacity tray I know of for these drives takes 48 SAS or SATA drives in 4U of rack space (about 7″ x 19″ x 24″).  You can sit multiple of these behind a single RAID box which would provide access for your computer over IP or FC depending on the type.

To get a real petabyte of base 2 usable storage you would need 546 2TB drives.  The whole setup including racks and power would weigh 1400kg or 3100lbs.  It would also consume 12kVA of power spitting out 39KBTU/hr of heat.

546 drives is for a PB of raw storage though.  In reality you would need to protect it from drive failures using RAID.  If we go for as littlle overhead as possible we can create 24 disk RAID 6 sets which would have about 40.4TB useable storage each.  For this we need about 600 drives which adds another 100kg to the weight.  Still about 1/180th of the weight of a PB just 30 years ago.