Advanced Format Drives
From 1956 up until recently, most disks used sectors of 512 bytes. Currently, the hard drive manufacturers are moving towards Advanced Formatting for their larger drives which use 4,096 byte sectors, or 4K sectors for short. This allows drives to write more data on the same space. Western Digital has a great two-page PDF file that explains Advanced Format. The link is in the show notes at http://www.wdc.com/wdproducts/library/WhitePapers/ENG/2579-771430.pdf
GPT partitioned disks actually have a “protective MBR” but it is only there to tell older utilities that the GPT partitions exist and not to erase or write over those areas. If you were to format the drive in MBR the system will only recognize the first 2048GB and leave the rest as unusable.
As you can see below, once a disk has been formatted as MBR, any space past the 2048GB is not usable.
For those of us that want 3TB or larger disks with 4K sectors, GPT is the only option. As a side note, the external 3TB drives you see currently in Best Buy and Fry’s translate the sectors so they can be used on any system.
In addition, GPT is not just made for large PC disks. I built a UEFI system with a single 300GB WD Raptor disk. Still not convinced? Need more proof?
Apple has been using GPT OS disks for years. APM, or Apple Partition Map, introduced in 1987 was replaced by GPT in 2006 when Apple moved to Intel CPUs. Mac OS X and later mount on GPT disks.
http://developer.apple.com/library/mac/#technotes/tn2006/tn2166.html
Windows Home Server and GPT
With Windows Home Server v1 and Windows Home Server 2011 there are a couple of issues.
Windows Home Server v1
First, with v1, you cannot use GPT disks at all. Diehard and I got a 3TB to be recognized in Disk Management using aftermarket Paragon software but the Console would always format and repartition a pool drive as MBR. The Console is designed to do that this so we could only get a 3TB drive to be recognized as a backup drive. Even then we were concerned about data safety and have given up until we hear back from Paragon.
Another issue with WHS v1 it that if you have a GPT client that backs up to a WHS v1, the backup will succeed but a standard Restore will fail.
Windows Home Server 2011
With 2011 there are a few concerns too. GPT disks are supported in Windows Home Server 2011 as storage disks but the Dashboard will split drives larger than 2040GB into multiple disks. You still get the full space but in multiple partitions. The reason is due to the fact that “dynamic or difference VHDs cannot exceed 2040GB. The reason for the 2040G limit is the length of each Block Allocation Table entry is set to 4 Bytes…If you multiply that value by 512B sector size and then subtract the overhead of on disk meta-data structures, 2040GB will be the maximum size of dynamically or differencing VHDs.” The Dashboard will convert any disk larger than 2TB to more than one partition to prevent a folder share from exceeding the maximum Windows Home Server 2011 backup size.
If you have a GPT client it CANNOT backup to Windows Home Server 2011. This means that if you have a GPT disk as your OS in a UEFI system, neither Windows Home Server version can back up or Restore your data. There is a GPT bug filed in Connect so if it is important to you then vote it up.
If you want to see GPT fully supported in WHS 2011 then go to Connect and vote up this bug too!
Anyway, enough of the short sermon. Check your new Sandy Bridge systems, your large format drives and your future build lists and let us know where you stand on GPT.
Timothy Daleo
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Additional References
http://msdn.microsoft.com/en-us/windows/hardware/gg463524
http://msdn.microsoft.com/en-us/windows/hardware/gg463525.aspx
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.