HP NetRAID Tutorial RAID Overview HP NetRAID Series adapters let you link multiple hard disk drives together and write data across them as if they were one large drive. With the HP NetRAID Series adapter, you can configure your linked drives into a RAID (Redundant Array of Independent Disks) subsystem. Physical Drive The term "physical drive" refers to a single hard disk module. Figure 1. Physical Drive Arrays HP NetRAID Series adapters can combine up to eight physical drives into one array.
Hot Spare A hot spare is a powered-on, stand-by disk drive that is ready for use should another disk drive fail. When a disk fails, the HP NetRAID adapter's firmware can automatically rebuild the data from the failed disk onto the hot spare. The system administrator can then replace the failed disk and designate the replacement as the new hot spare disk. Until a rebuild occurs, a hot spare does not contain user data.
Figure 3. Sample Configuration with Three Arrays and Three Logical Drives Understanding RAID Levels During installation, you configure your logical drives by running a disk array configuration utility. Each of the logical drives you define must have an assigned RAID level. Each RAID level has different advantages in terms of performance, redundancy, and capacity. HP NetRAID Series adapters support both nonspanned array and spanned array configurations.
Arrays with No Redundancy: RAID Level 0 RAID 0: Striping In RAID 0 configurations, data is distributed among hard disks in the array via an algorithm called striping. Data written to a logical drive is divided into pieces called blocks. RAID 0 provides no data redundancy. If one hard disk fails, the data is lost from the entire logical drive and must be retrieved from a backup copy.
Non-spanned Arrays with Redundancy: RAID Levels 1, 3, and 5 RAID 1: Mirroring In RAID 1 configurations, data on one disk is completely duplicated on another disk. This is called mirroring. RAID 1 must be configured on a two-disk array. (The array cannot contain more than two disk drives.) With this algorithm, if either of the two disks fail, data is available from the duplicate disk.
RAID 3: Striping with Dedicated Parity In RAID 3 configurations, each data stripe generates one parity block to provide redundancy and data protection. The parity block is encoded information that can be used to reconstruct the data on that stripe if one of the disks fails. RAID 3 configurations dedicate one disk in the array to store all parity blocks.
RAID 5: Striping with Distributed Parity RAID 5 is the most common configuration because it provides good overall performance and data protection with a minimum loss of storage capacity. RAID 5 distributes the parity blocks equally among all disk drives to achieve better overall performance than if a dedicated parity disk is used (RAID 3).
Spanned Arrays: RAID Levels 10, 30, and 50 With HP NetRAID Series adapters, array spanning allows the capacity of two, three, or four arrays to be combined into a single storage space. A spanned array configuration must have the same number of disk drives in each array: each array can have two disks, three disks, four disks, and so on. RAID 10: Spanning with Mirrored Arrays A RAID 10 configuration uses two, three, or four pairs of mirrored disks, spanning two, three, or four arrays, respectively.
RAID 30: Spanning with Dedicated Parity Drives In RAID 30 configurations, parity blocks provide redundancy to a logical drive that spans two, three, or four arrays. (RAID 30 is a RAID 3 configuration with array spanning.
RAID 50: Spanning with Distributed Parity In RAID 50 configurations, parity blocks are distributed throughout the logical drive that spans two, three, or four arrays. (RAID 50 is a RAID 5 configuration with array spanning.
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Figure 4. Decision Tree for Choosing a RAID Level Rebuilding and Reconstructing Data With HP NetRAID Series adapters, the terms "rebuilding" and "reconstructing" refer to different processes. • Reconstructing data is the process of reorganizing data to correspond to a change in the HP NetRAID system. Reconstruction is necessary if you change a logical drive from one RAID level to another, or if you add or remove a disk drive from an existing logical drive.
logical drives (RAID levels 1, 3, 5, 10, 30, or 50.) Data in RAID 0 logical drives cannot be rebuilt, and must be restored from a backup copy. More About Rebuilding Data A configuration of RAID 1, 3, 5, 10, 30, or 50 has built-in redundancy. If a drive in one of these RAID levels fails, the RAID subsystem continues to operate, but no additional redundancy is provided and the logical drive becomes "degraded." Another drive failure will cause data loss.
