Support for 3TB hard drives
The capacity of hard drives (HDD) is growing and growing. In the past years we have experienced the move from 300GB to 500GB, 1TB, 1.5TB, 2TB, and now 3TB. We did not see any issue in the moves until 2TB. Why does increasing to 3TB in capacity become a topic?
To answer this question, let’s do some math. The HDD industry used to use 512 bytes per each sector. To use all spaces in the HDD, the controller needs to address all these sectors in the HDD. In the era of 32-bit, the total addressable space is:
2 ^ 32 x 512 (bytes) = 2,199,023,255,552 (bytes)
Which is approximately 2.2TB. So, the drive with a capacity greater than 2.2TB (say, 3TB) is over this addressable limit.
There are two ways to break this limit:
(1) Use a 64 bit controller to address the sectors.
(2) Increase the bytes per each sector from 512 Byte to 4kB.
Some older controllers (e.g., OXE-92X series) cannot support 64-bit address, nor the 4kB per sector. In this case, there is no way to support a 3TB HDD. In most of our products, we can adopt either or both of these two solutions. There are advantages and disadvantages to adopt either one of them.
Increase the addressable sectors from 32 bit to 64 bit. In this case, we can support all existing HDDs (512 bytes/sector in most cases; 4kB/sector in newer models). Modern operating systems (WinXP-64bit, Vista, Win7, Linux, MacOS) use 64-bit so it is not a problem. However, old operating systems which use 32-bit (e.g., WinXP-32bit) cannot work with this solution. If we adopt this option, any user who wants to access a 3TB HDD needs to have one of the newer operating systems.
Force the SATA bridge to use 4kB/sector to read/write data to HDD, while keep using 32 bit address. In this case, all operating systems can see the 3TB HDD. However, when users install an older HDD (e.g., 1TB, with 512 bytes/sector) the bridge cannot work.
Option 2 is suitable to HDD manufacturers such as Seagate and Western Digital, who ship the enclosure with a known HDD and do not allow users to replace the HDD. Option 1 is more appropriate for most of inXtron's customers. However, the end user needs to be made aware that older operating systems like WinXP-32bit cannot support 3TB volumes and that if the user wants to upgrade the storage capacity to 3TB, a newer operating system is required.