The woes of a GUID Partition Table

[John A]

GPT, an acronym for GUID Partition Table, is likely something you've never heard of before. Perhaps that's a good thing. Throughout my usage of GPT, I've come to see that it's a total and complete waste of time.

What is GPT, anyway? Wikipedia defines it as a partition layout standard for a hard disk. They go own to say that "it is a part of the Extensible Firmware Interface (EFI) standard proposed by Intel as a replacement for the outdated PC BIOS, one of the few remaining relics of the original IBM PC."

GPT actually features a number of improvements over the old Master Boot Record (MBR) method of partitioning used with PC BIOS. You might recall that MBR-based partition tables have a limit of 4 primary partitions. The user is then forced to create an extended partition in order to expand the limits. GPT on the other hand, has a limit of by default, 128 primary partitions. And because of this huge amount, Intel thought it was rather pointless to have extended partitions. One other important feature of GPT is that it has two tables: a primary one, and a secondary one, for backup purposes.

Great! So how come everyone isn't using this obvious improvement? Well... let's see. GPT isn't backwards-compatible, therefore PC BIOSes are incapable of booting GPT-enabled disks. And there's actually a very limited range of machines that have EFI, so this is probably the biggest reason why GPT isn't used.

Except for Macs. Apple has decided to use them in all of the Intel Macs. That sounds like an obvious improvement, right? Not. The most important use of a partition is for holding an operating system, correct? That's wonderful, when GPT is so poorly-supported by most operating systems. I'm serious, only a handful of operating systems support them, and Windows is not one of them. So that basically takes away the whole point of GPT, does it not?

Ah, but I forgot something. Intel designed the GPT so that it can exist alongside an MBR partition table. In other words, a special utility called gptsync can sync the MBR to the GPT, creating backwards compatibility with legacy operating systems. Except there's a catch: remember how it was mentioned that MBR can only support 4 primary partitions? And how GPT doesn't support extended partitions? That's right, you're limited to exactly 4 partitions with a MBR/GPT hybrid partition table. Kind of takes away the point of GPT, doesn't it? To make matters worse, the syncing is a one-way process: you can't edit the MBR and sync the GPT to it. Therefore, changes you make to your partition table must be done with a partition tool that supports GPT. Oh brother.

Some of the readers may be saying, "Ah, but what does it matter? Macs are one of the largest EFI-enabled computers, and how many Mac users edit their partition tables?" I'd like to point out that the people who don't edit their partition tables won't care if it's MBR or GPT anyway. For the ignorant people, GPT won't make an ounce of difference. And it creates nothing but a hinderance for those who actually want to utilize it.

And, let me point out that GPT isn't necessary on EFI-enabled systems. Indeed, EFI systems are just as capable of booting from MBR disks as any regular PC is. Great, Apple, just great. Do as all a favor and stop using this crap from Intel.

[mab93]

I think you are not giving GPT a fair review. In order to move to newer technology someone needs to start taking advantage of it's features or we would never be able to advance technology.

You said that "only a handful of operating systems support them, and Windows is not one of them". First, the 64 bit version of windows and windows vista do support GPT (http://www.microsoft.com/whdc/device/storage/GPT_FAQ.mspx). Second, by "only a handful", you must mean the common ones such as Linux, and BSD Unix. Aside from XP the only OSes that don't support GTP are old ones and ones who's development is slow. Windows just decided not to put it into XP.

My only real issue is that they don't allow extened partitions for a mixed GPT/MBR situation. I think the primary partition / extended partitions should eventually be eliminated, but a better transition plan should have been made. Some better tools would be nice too, but that usually comes with time.

I have a triple boot Mac and have run into some GPT/MBR problems too. I parted on my hard drive from linux and it wiped out my MBR partition table. It was easy to get back though.

[mathematician]

The reason a new style of partition table is needed is simply that the MBR style of partition table won't be able to cope once hard disk capacities atart to exceed 2Tb, as they shortly will.

[bitsltd]

GUID partition tables will work with any computer & it a major improvement over MBR. The only problem is that Microsoft & the drive partition tools companies have been slow to implement it. It is supported under XP x64, Vista, Windows 7, Microsoft server 2003 & newer, all unix/linux variations & Intel macs. So it is only not supported by OLDER operating system before it was invented. It is like saying NTFS is bad because windows 3.11 does not support it. The EFI header is a virtual bios that can be setup to allow MOST ANY operating system to work on MOST any computer by emulating the required bios so the computer bios itself does not need to have the correct bios for that OS. Before bashing something you need to really understand what you are bashing.

[Jon Pierce]

I sympathize with all the posts here. The OP is correct about his complaints. But the other poster's points also stand - the future is GPT but Microsoft has been slow to implement it.

[jbennet]

the future is GPT but Microsoft has been slow to implement it.

The Itanium versions of windows XP/2003 intall on EFI.

[STEVON-SD]

Like any new complicated technology, it often requires learning new skills. To enjoy it's benefits takes time and effort. Study, try, fail, try again then conclude an informed opinion. In my case I'm building a HTPC that captures and encodes HD video and sound into .264 files. This requires a large (Striped) fast hard drive array to process and store 10 gig or so of HD streaming data an hour. Setting up 2 Seagate 1.5 SATA drives in RAID 0 yields a 2.7 TB partition. Getting Windows 7 to boot on any partition on that volume was not possible without extra partitions with software spanning of 2 of the 3 Windows required partitions. There goes the advantage of one large fast volume. The solution was to disconnect the RAID 0 array drives, intall a new smaller 3rd hard drive and load Windows 7 (32 or 64) with all RAID and AHCI drivers for the RAID controller. Shut down the system, reconnected RAID 0 drives, booted system, went into BIOS and set 3rd hard drive to boot first (MBR location). When Windows 7 booted it saw the new array as a 2.7 TB drive with 2 partitions available, one at 2 TB and another at 700 Gb. This shows the 2 TB MBR limit. In disk Management right click on Disk 1 (RAID 0 volume) and convert to GPT. Next name the volume, select cluster size (I chose 8kb clusters for 2 to 4 TB volumes), format, finish. I now have a perfect, usable 2.7 TB windows data partition that could NOT EXIST without GPT option! In my case GPT was needed and worked great for the large fast volume. It's too bad it took 4 days to figure out how to use GPT with Windows!
MBR is like IPV4, useful indeed but a better option will have to come like GPT and IPV6. You can't stop progress, the world is changing too fast!
Stephen

GPT, an acronym for GUID Partition Table, is likely something you've never heard of before. Perhaps that's a good thing. Throughout my usage of GPT, I've come to see that it's a total and complete waste of time.

What is GPT, anyway? Wikipedia defines it as a partition layout standard for a hard disk. They go own to say that "it is a part of the Extensible Firmware Interface (EFI) standard proposed by Intel as a replacement for the outdated PC BIOS, one of the few remaining relics of the original IBM PC."

GPT actually features a number of improvements over the old Master Boot Record (MBR) method of partitioning used with PC BIOS. You might recall that MBR-based partition tables have a limit of 4 primary partitions. The user is then forced to create an extended partition in order to expand the limits. GPT on the other hand, has a limit of by default, 128 primary partitions. And because of this huge amount, Intel thought it was rather pointless to have extended partitions. One other important feature of GPT is that it has two tables: a primary one, and a secondary one, for backup purposes.

Great! So how come everyone isn't using this obvious improvement? Well... let's see. GPT isn't backwards-compatible, therefore PC BIOSes are incapable of booting GPT-enabled disks. And there's actually a very limited range of machines that have EFI, so this is probably the biggest reason why GPT isn't used.

Except for Macs. Apple has decided to use them in all of the Intel Macs. That sounds like an obvious improvement, right? Not. The most important use of a partition is for holding an operating system, correct? That's wonderful, when GPT is so poorly-supported by most operating systems. I'm serious, only a handful of operating systems support them, and Windows is not one of them. So that basically takes away the whole point of GPT, does it not?

Ah, but I forgot something. Intel designed the GPT so that it can exist alongside an MBR partition table. In other words, a special utility called gptsync can sync the MBR to the GPT, creating backwards compatibility with legacy operating systems. Except there's a catch: remember how it was mentioned that MBR can only support 4 primary partitions? And how GPT doesn't support extended partitions? That's right, you're limited to exactly 4 partitions with a MBR/GPT hybrid partition table. Kind of takes away the point of GPT, doesn't it? To make matters worse, the syncing is a one-way process: you can't edit the MBR and sync the GPT to it. Therefore, changes you make to your partition table must be done with a partition tool that supports GPT. Oh brother.

Some of the readers may be saying, "Ah, but what does it matter? Macs are one of the largest EFI-enabled computers, and how many Mac users edit their partition tables?" I'd like to point out that the people who don't edit their partition tables won't care if it's MBR or GPT anyway. For the ignorant people, GPT won't make an ounce of difference. And it creates nothing but a hinderance for those who actually want to utilize it.

And, let me point out that GPT isn't necessary on EFI-enabled systems. Indeed, EFI systems are just as capable of booting from MBR disks as any regular PC is. Great, Apple, just great. Do as all a favor and stop using this crap from Intel.

[Tilipitappi]

Hello. Sorry to bring this ancient thread to life but since it's the third hit on googling GUID partition table, I feel I need to correct two invalid assertions made by the original poster in the statement "GPT isn't backwards-compatible, therefore PC BIOSes are incapable of booting GPT-enabled disks".

Disk contents are not in the domain of the BIOS except for looking for a 55AAh bootable flag in the first sector of the disk and loading the first sector into 07C0h. GPT is written starting from the second sector so it does NOT interfere with MBR operation, and is thus backwards compatible where the BIOS and an MBR bootstrap are concerned. In fact this is beneficial for the bootstrap programmer since eliminating the traditional partition table frees up more space for the program; 510 bytes instead of 440. There is an exception to this case, however, where the GPT is protected from old MBR and FS utils that might erroneously write over the GPT by making a traditional partition and a filesystem to follow: create a traditional partition that spans the whole disk and flag it as EEh (GPT partition type). Old tools and intelligent tools should recognize this as an unknown partition and will not touch it. After the bootstrap it's entirely the problem of the OS whether it can understand GPT or not. Most modern operating systems can, but this is definitely not a BIOS or MBR related issue.