Disk Storage

Hardware RAID arrays abstract the physical combination of disks, presenting logical disk volumes to the Operating System. A logical volume is a basic unit of storage, which may consist of several disk or just a portion of one disk. You can assign one or no drive letter to a volume, and/or mount a volume to an empty folder on another NTFS volume. Server 2003 provides two types of fault tolerant volumes: RAID1 and RAID5. Software RAID using system resources and does not perform as well as hardware RAID. Normally separate volumes are assigned to system, application and data volumes, allowing appropriate configuration of storage requirements for each (security, size, fault tolerance, performance).

Basic Disks

Stores partition information in MBR. May contain four primary partitions or three primary and one extended. Each primary partition contains one logical drive, extended partitions may contain one or more logical drives. Only one primary partition can be active. Basic disks are the default in Windows 2003: no benefit from having dynamic disks when machine has only one physical disk.

Dynamic Disks

Dynamic disks (Windows 2000, XP, 2003) support an unlimited number of volumes. Configuration is stored in a database controlled by Logical Disk Manager service. Dynamic disks support simple volumes on a single disk. When converting from dynamic to basic disk all existing volumes must be deleted, therefore all data is lost. Multiple dynamic disks can be combined into:

Spanned Volume

combines free space from up to 32 disks, data written to first disk until that fills up, then to second disk, and so on. Spanning provides no fault tolerance, and is in fact more prone to failure than simple volumes: failure in any one disk in a spanned volume, will result in the whole volume failing. Windows 2003 will not install to a spanned volume, nor can you extend or span an existing system volume. Recommended only as a stop gap measure or where tolerance for failure is high.

Striped Volume

(RAID 0): combines equally sized volumes from multiple disks into one logical volume. Data written to all physical disks at same rate. Because multiple spindles are in use, greater performance is achieved than with spanned volumes, but failure in one disk will cause whole volume to fail.

Mirrored Volume

(RAID 1): two identical copies of a simple volume, each on separate disks. Provides fault tolerance with 50% overhead

RAID5 volume

Fault tolerant striped volume. requires three or more physical disk. data written to all disks at same rate, interlaced with checksum information (parity). If one disks fails it can be regenerated with remaining data and parity information. Parity is distributed amongst all volumes, but total overhead for fault tolerance is equal to one/numberOfPartitions used. Calculation of parity decreases performance compared to mirror when writing data, but read performance improved as multiple spindles are used. An existing volume cannot be converted to RAID 5: data must be backed up, RAID5 created, and then data restored. When a disk fails in a RAID5 volume, all read operations require that the data is regenerated on the fly using remaining data and parity, hence performance degraded

Windows 2003 does not support arrays created on NT4, nor will it allow you to extend volumes created in Windows 2000.

Disk Management Console

Disk management console uses the Logical Disk Manager Administrative (dmadmin) service to configure disks. dmadmin is started when diskmgmt used to connect to either local or remote disks. Only administrators can format a volume. If a new drive is not detected automatically, right-click the disk management node and choose Rescan Disks. Before allocating disk space, the disk should be initialised (write a disk signature, end of sector marker and an MBR or GUID partition table). Initialisation should occur automatically, but is also available as an action in diskmgmt. Use mount points or extend option to increase size of an existing logical drive. With basic disks you can only extend to an immediately contiguous space on the same disk.

Moving Disks

1. Check disk is healthy
2. Uninstall disk with devmgmt
3. (dynamic disks only) in diskmgmt, right-click disk and choose Remove
4. attach disk to new server
5. choose Rescan if necessary
6. Found New Hardware wizard should start, or PnP detection will automatically install the disk. otherwise run Add/Remove hardware to detect the disk
7. choose Import foreign Disk

Command Line Tools

chkdsk, convert, fsutil, mountvol and diskpart. Sample Diskpart commands:

• list disk
• list partition
• list volume
• create volume simple size=500 disk=2
• select volume 4; assign letter j
• select volume 4; extend size=250 disk=2 (extends disk, assuming volume 4 is on disk2)
• select volume 4; extend size=250 disk=1 (spans disk)
• delete volume
• assign mount=e:\folder1
• create volume stripe size=500 disk=1,2
• create volume simple size=500 add disk 2 (create mirror)
• break disk 2 (remove disk 2 from mirror)
• break disk 2 nokeep (remove disk from mirror, erase all data)
• create volume raid size=500 disk=1,2,3
• convert dynamic
• convert basic

Defrag

defrag on 2003 improves on 2000 by enabling defragmentation of: MFT and; volumes with cluster sizes larger than 4KB. Does not support defragmentation of remote volumes or scheduling. Requires 15% free space on volume, may require more if the volume contains a lot of large fragmented files. Partial defragmentation only available if free space less than 15%.

Quota Manager

Quota manager tracks disk usage by owner. Displays free space on volume as free quota space. Quotas disabled by default on Windows 2003. Enable quotas using quota tab on properties page for volume. Then set quota defaults and exclusions. Use diskmgmt to set quotas for mounted volumes. Administrators have 'No Limit' configured as the quota entry. Quota manager does not support assigning quotas to groups or on folders: must be per-user and per-volume.

Disk Recovery

Recovering Raid 0: recreate and restore from backup

Recovering RAID1: remove mirror from bad disk, then add mirror from good disk when new disk available

Recovering RAID5: replace disk, rescan, initialise, convert to dynamic disk, then choose repair volume and select new disk to add