If you have dealt with HP Smart Arrays, you are familiar with the term ?stripe size?. It?s one of the parameters you set when configuring a new logical drive. During the next year, you will find the term ?stripe size? replaced with ?strip size? in Smart Array-related configuration utilities and documentation. Is something really changing here? Not really, only the terminology is changing. But before explaining the reason for the change, let?s quickly review some RAID basics.
Stripe size versus strip size
An array consists of two or more physical drives that are configured together through a RAID controller to appear as a single logical drive to the OS. To improve overall performance, RAID controllers break file data up into discrete chunks called ?strips? that are distributed one after another across the physical drives in the arrays. In Figure 3-1, each individual unit — A1, B1, or B2, for example — represents a strip. For a given array, the strip size is configurable, typically between 64 KiB and 256 KiB.
A stripe, on the other hand, is the collection of one set of strips across the physical drives in a logical drive. A stripe?s size is not configured. It is a product of the strip size, the number of physical drives in the logical drive, and the RAID level. In Figure 3-1, a stripe is represented by each color band across the physical drive set. If the strip size in this logical drive is 256 KiB, then the stripe size is three times that, or 768 KiB. The parity strip — represented by Ap, Bp, etc. in Figure 3-1 — is not considered part of the stripe?s size although it is part of the structure. The stripe size for a RAID-5 and RAID-6 array is the same, even though there is twice as much parity data.
Changing terms to strip size
HP Smart Array utilities have traditionally used the term stripe size as a configuration parameter when, in terms of standard RAID definitions, it?s the strip size that?s actually being configured. In order to differentiate between the two, HP documentation has sometimes referred to the RAID stripe as the ?full stripe?. But starting soon, HP Smart Array utilities, including ORCA and ACU, will be migrating to the use of the standard RAID terms of strip size and stripe size. This change will be incorporated over time as new releases of the utilities are required. So don?t be surprised someday soon when you open the ACU to find that you are setting the strip size and not the stripe size.
|Additional resources Resource||URL|
|Home page for HP Smart Array controllers||http://h18004.www1.hp.com/products/servers/proliantstorage/arraycontrollers/index.html|
|Storage Networking Industry Association online dictionary||http://www.snia.org/education/dictionary/|