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Reviewing Storage Limits

Updated: August 3, 2011

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2, Windows Server 2008, Windows Server 2008 R2, Windows Server 2008 R2 with SP1

To accurately plan for storage scalability, you must take into account the physical and logical design limits of your servers. The following sections describe these limits.

Reviewing the physical storage limits

From a hardware perspective, your choice of storage bus will determine the physical limits of your storage scalability. For example, local storage with two Integrated Device Electronics (IDE) controllers will allow a system to have up to four IDE storage devices; with SCSI storage, the SCSI bus type will determine the maximum amount of allowable storage devices on each bus. If you need to extend a system’s local storage beyond the limitations of IDE or SCSI, you can use Fibre Channel–based storage or use SCSI protocol over TCP/IP (iSCSI), a new IP-based storage networking standard that carries SCSI commands over IP networks. However, these newer, more flexible architectures are more expensive than traditional IDE or SCSI buses.

ImportantImportant
Unless otherwise noted, all storage limits discussed in the following sections apply to Windows Server® 2003, Windows Server® 2008, and Windows Server® 2008 R2 operating systems.

Reviewing the limits for basic and dynamic Disks

In addition to reviewing the physical storage limits, you also need to keep in mind the volume types in Windows Server 2003, Windows Server 2008, and Windows Server 2008 R2 and their limits. All versions of these operating systems provide enhanced volume management capabilities. You can plan for both basic disks and volumes and dynamic disks and volumes.

Basic disks use the same disk structures as those used in Microsoft® Windows NT® version 4.0 and Windows 2000. When you use basic disks, you are limited to creating four primary partitions per physical disk, or three primary partitions and one extended partition that can contain multiple logical drives. Primary partitions and logical drives on basic disks are known as basic volumes. As shown in Table 1.2, basic volumes are limited to 2 TB. Even if you create multiple volumes on a single logical unit, the combined size of all those volumes cannot exceed 2 TB. If you want to use volumes larger than 2 TB, you must use dynamic spanned, striped, or RAID-5 volumes.

Dynamic disks, which offer features not available in basic disks, were introduced in Windows 2000. Dynamic disks contain dynamic volumes, including simple volumes, spanned volumes, striped volumes, mirrored volumes, and RAID-5 volumes. Dynamic disks offer greater flexibility for volume management because they use a hidden database, instead of the disk’s partition table, to track information about dynamic volumes on the disk and about other dynamic disks in the server. This flexibility allows you to create spanned, striped (RAID-0), and RAID-5 volumes that exceed the 2-TB size limit of basic volumes. Simple and mirrored volumes cannot exceed 2 TB.

Table 1.2 lists the contrasts between basic and dynamic Master Boot Record (MBR) disks.

Table 1.2   Comparison of Basic and Dynamic MBR Disks

 

Storage Capabilities Basic Disks Dynamic Disks

Volume size (maximum)

2 TB

2 TB for simple and mirrored volumes.

Up to 64 TB for spanned and striped volumes. (2 TB per disk with a maximum of 32 disks per volume.)

Up to 62 TB for RAID-5 volumes. (2 TB per disk with a maximum of 32 disks per volume and 2 TB used for parity.)

Supported RAID implementation

Hardware RAID only

Hardware or software RAID

Storage of boot and system volumes

Yes

Simple or mirrored volumes only

Shared cluster storage in server clusters

Supported

Not supported*

* For more information about using dynamic disks on shared cluster storage, see article 237853, in the Microsoft Knowledge Base (http://go.microsoft.com/fwlink/?linkid=99316).

Use the following guidelines to choose between basic disks and dynamic disks.

Use basic disks if:

  • You do not need to create volumes that exceed 2 TB.

  • You are configuring shared cluster storage on a server cluster.

  • The server runs other operating systems that cannot access dynamic disks. The only server operating systems that can access dynamic disks are Microsoft® Windows® 2000 Server and Windows Server 2003.

Use dynamic disks if:

  • You want to create RAID-0 volumes or fault-tolerant volumes (RAID-1 or RAID-5) and the server does not contain hardware RAID.

  • You want to combine logical units (LUNs) in a RAID array to create a volume larger than 2 TB.

  • You want to extend a volume, but the underlying hardware cannot dynamically increase the size of LUNs, or the hardware has reached its maximum LUN size.

Reviewing the limits for NTFS and the number of volumes per server

When you configure storage in Windows operating systems, it is important to understand NTFS limits and volume limits for server storage.

Table 1.3 describes the NTFS and volume limits.

Table 1.3   NTFS and Volume Limits

 

Description Limit

Maximum size of an NTFS volume

232 clusters minus 1 cluster

Using a 64-kilobyte (KB) cluster (the maximum NTFS cluster size), the maximum size of an NTFS volume is 256 TB minus 64 KB.

Using a 4-KB cluster (the default NTFS cluster size), the maximum size of an NTFS volume is 16 TB minus 4 KB.

Maximum number of dynamic volumes per disk group

1,000

A disk group is collection of dynamic disks. Windows Server 2003 supports one disk group per server.

Maximum volumes per server

Approximately 2,000 volumes

Up to 1,000 of these volumes can be dynamic volumes; the rest are basic volumes. Boot times increase as you increase the number of volumes. In addition, the use of multipathing can reduce the number of volumes per server.

Reviewing the number of supported disk drives

When you select the number of disk drives in Windows operating systems, it is important to understand the number of drives supported in different types of file systems. The number of disk drives you can use for each server is limited only by the available memory for FAT16, FAT32, NTFS, and UDF files systems.

Reviewing methods for adding storage space to volumes

If you create volumes smaller than the maximum sizes listed earlier, and you later want to add storage space to those volumes, you can do so by increasing the size of the volume or by creating a mounted drive.

Extending volumes

When a defined volume begins to reach its allocated capacity, but there is still free unallocated space on a hard disk or hardware RAID array, you can use the DiskPart command-line tool (Diskpart.exe), available in the Windows Server 2003 operating system, to extend the volume size without any loss of data. When using DiskPart, consider the following guidelines:

  • You cannot use DiskPart to extend system or boot volumes; DiskPart can only be used to extend data volumes. This is not applicable for Windows Server 2008.

  • The volume to be extended must be formatted with the NTFS file system.

  • For basic volumes, the unallocated disk space used for the extension must be the next contiguous space on the same disk. (The disk can be a single physical disk or a group of physical disks presented by a RAID adapter to the operating system as a single disk, often referred to as a LUN.)

  • For dynamic volumes, the unallocated disk space can be any empty space on any dynamic disk on the system.

  • If you upgraded from Windows 2000 to Windows Server 2003, you cannot extend a simple or spanned volume that was originally created as a basic volume and converted to a dynamic volume on Windows 2000. For more information about basic and dynamic volumes, see Storage Technologies Collection (http://go.microsoft.com/fwlink/?linkid=4681).

For more information about using DiskPart, see "DiskPart" in Help and Support Center for Windows Server 2003. For more information about choosing volume sizes based on Chkdsk and recovery times, see "Designing and Deploying File Servers" in this book.

Using mounted drives

Mounted drives are useful when you want to add more storage to an existing volume without having to extend the volume. A mounted drive is a local volume attached to an empty folder on an NTFS volume. Mounted drives are not subject to the 26-drive limit imposed by drive letters, so you can use mounted drives to access more than 26 drives on your computer. For more information about mounted drives, including information about creating mounted drives on server clusters, see "Using NTFS mounted drives" in Help and Support Center for Windows Server 2003.

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