What is the Disk Capacity and Partition Amounts for GPT and MBR

08 September,2021 by Rambler

Question: I've reached some drive storage limits on SQL Server supporting large modelling databases. There is plenty of underlying storage available but the current disk is initialized with MBR. Could you explain the differences in disk capacity and partition amounts for GPT and MBR

Answer:  GPT (GUID Partition Table) and MBR (Master Boot Record)  are partitioning schemes - so doing the same thing i.e managing partitions, but some key differences, especially around support on disk capacity and partition Amounts.

(From Microsoft Doc)  "Master Boot Record (MBR) disks use the standard BIOS partition table. Maximum of 4 primary partitions . If more are required , an extended partition is required."

If a disk is initialized to MBR , there is a limit of 2 TB or 16TB. This depends on whether you used the traditional 512B sector - limited to 2 TB. If using the 4K native, you can use 16TB. 

(From Microsoft Doc) "Partition Table (GPT) disks use Unified Extensible Firmware Interface (UEFI).IN theory an unlimited number of partitions but Windows has a 128 partition restriction limit. Any GPT partition can operate like a primary partition"

If a disk is initialized to GPT the disk can be up to 2^64 logical blocks in length. This can grow to a significantly larger size than MBR 


Using this information - GPT is required for disks larger than two terabytes (TB).  Before you start thinking about converting a disk - backup the data or move the data

If you're commiting to an inplace Delete Partion\Delete Volume & Covert to GPT Disk , it will wipe the data on the volume

Author: Rambler (http://www.dba-ninja.com)


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