In this episode we talk about GPT and Master Boot Record formatting and this short sermon gives you a brief overview of these types of technology. Read on to find out how the use of drives larger than 2.2TB will affect your systems.
Master Boot Record Limits
The MBR is used for booting your operating system and holding your disk’s primary partition table. Think of it as a tiny bit of space at the “front” of your disk that that tells the disk and your PC how to use the disk. The MBR stores this information in 32-bit sectors, but because the sector size is only 512 bytes, you are limited to a disk space of 2.2 TBs. I have mentioned on BYOB before, take the 512 bytes x 232 (for 32 bit) and you get the magical 2.2TBs. 4,294,967,296 x 512 gives us the 2.199TB. Make sense now? This is a mathematical limitation.
In addition, another limit to MBR is that you can have at most only four primary partitions. GPT disks in Windows can have up to 128 primary partitions!
It is for these and other limits that the GPT scheme becomes important.
With drives under 2.2TB the math is not an issue, but since companies like Dell and HP are already offering systems with single 2TB drives, large format OS drives are on the horizon.
GPT
A GPT formatted disk, or a GUID Partition Table disk, is the replacement layout for BIOS based MBR on hard disks. As MBR disks are limited to 2.2TB, GPT disks are “limited” to 9,444,732,965 TB or 9.4 ZB. We are not going to be seeing drives hitting that maximum any time soon.
Converting drives in Windows Disk Management is as easy as a right mouse click when installing the drives. If needed, you can convert from GPT to MBR and back again, but any data on the disk will be destroyed. This means you can move disks, but not the data, between the formats.
I put two 3TB drives in my Windows Home Server 2011 and they perform great.
GPT has actually been around since the 90’s and has been supported by Microsoft since Windows Vista. Yes, every 64-bit Windows installation DVD since Vista has included support for UEFI and GPT disks.
Some GPT facts:
- 32-bit Windows machines do not support GPT
- GPT is only supported as a boot disk in a UEFI environment
- Windows only supports NTFS with GPT
- Windows XP supports only MBR partitioning on detachable disks.
- Removable media must be MBR or “superfloppy.”
So I have established that GPT drives can be bigger than MBR drives so what? Why do BYOB listeners care? Well, as these new drives become mainstream they will filter into the OEMs and retail and be available to everyone. Even today, 02-27-11, BestBuy has 3TB drives on sale for $150 now. Imagine your next HTPC with a single low power 3TB drive that could contain your entire media collection.
The more we know now, the better prepared we can be and even design our systems for growth.
thanks Tim – what is the URL for the Connect bug so we can all vote it up?
Thanks for adding both links 🙂
Come on people, vote on these!
I’ve voted, but frankly, I don’t hold out much hope for a worthwhile response from the WHS team.
Tim and I will both be bringing this up with the team this week while we are here in Seattle!
Thanks Andrew – good luck in talking to the team. On an associated note, it looks as though the process for making off-site backups in WHS2011 could do with some attention as well. See:
https://connect.microsoft.com/WindowsHomeServer/feedback/details/647990/backup-stopped-due-to-insufficient-disc-space-even-though-every-storage-disc-had-at-least-one-backup-disc-of-equal-or-greater-size
I love the way in which the “Backup best practices” section of the WHS2011 help documentation states:
“Use an external hard disk with at least 1.5 times the storage capacity of the items that you want to back up”.
So, with my Movies folder already at 2TB, then I should be using a 3TB drive to back it up? Oh, that’s right, I can’t…
What if you have a non-GPT drive (1 TB) but are using a UEFI system? Will the backup and restore feature work in this scenario?
I have not tried a UEFI installation on a MBR disk. I know that the Michaels have sandy bridge systems that run UEFI but on regular disks. I will check with them to see, but I believe they had issues with backup too. More testing needs to be done since a 100MB EFI System Partition (ESP) and the 128MB Microsoft Reserved partition (MSR) are created during UEFI installations. Will update you via comments as soon as I find out. Martis may know too, so try a HSS post if you need more information before I get back.