The problem with striping on Raid is that the files are broken down into segments that are spread across the drives that are installed. The following outlines the process in greater detail.
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Striping
Stripping is a feature of a RAID configuration that offers huge performance gain. Data in a striped array is written or read across all the array drives simultaneously. When the computer writes data into the disk, the data is divided across several pieces and inserted into each individual disk at the same time. Similarly, when the computer request to read a file, the multiple pieces of data from each disk drive are extracted together to be processed by the CPU, which effectively increases read/write time. Striping involves partitioning each drive's storage space into units which are known as the stripe block size.
There're two important variables in a striped array, namely the stripe width and stripe size. Both factors greatly determine the performance of a striped array.
- Stripe Width:
The stripe width refers to the number of drives in the array.
- Stripe Size:
The stripe size represents the size of a single chunk of unit data to be written into each disk. The stripe size is configurable and can range from 512 bytes to several megabytes. The default IDE configuration is 64K. It is commonly a multiple of 8k.
To demonstrate this, assume we need to write a 5MB file into a disk array. If we have an array of 5 drives and writing the data at 100K per unit, we'll need 10 write cycles to complete writing the entire file. Note that each cycle only writes 500K of the file. Now if we have an array of 10 drives, we can effectively reduce the write time into half since each write cycle writes 1MB of the file. This will also mean that only 5 write cycles are needed to complete writing the file. So generally, we can see that the more drives that are implemented, the faster its performance. It is also apparent that for larger data size, increasing the strip size will help.
However, there're certain factors that must be considered when selecting the stripe width and stripe size.
Firstly, if the stripe size is too small, writing a big file would cause the file to be broken down into many segments across the drives hence utilizing more disk resources. A stripe size too big may exceed the size of the data to be stored and result in space wastage. That is to say if you configure 100K as your stripe size, you'll waste 30K of space if you are to write a 70K sized data.
Generally, the more drives that are implemented, the better its the performance. However if any one disk breaks down, all data will be lost. This reliability is often measured by mean time between failure (MTBF), which is a inverse proportion to the stripe width. That is to imply that a set of 3 disks is 1/3 as reliable as a single disk. Hence, increasing the number of disk drives in the array for data stripping will also increase the risk of a disk failure.
The drawback of using striping is that similar hard disks must be used together in the array to prevent latency. As the data parts are read from the various drives to be pieced together to form the original data, the slowest drive will determine when the concatenation completes." http://www.datarecovery.com.sg/data_recovery/types_of_raid_configurations.htm
One thing seen at Microsoft Technet will be useful here since in order to create a spanned volume across mulitple hard drives you have to have and NTFS type partition to begin with.
Spanned Volumes
Spanned volumes combine areas of unallocated space from multiple disks into one logical volume. The areas of unallocated space can be different sizes. Spanned volumes require two disks, and you can use up to 32 disks. When creating spanned volumes, keep these points in mind:
•You can extend only NTFS volumes or unformatted volumes.
•After you create or extend a spanned volume, you cannot delete any portion of it without deleting the entire spanned volume.
•You cannot stripe or mirror spanned volumes. For more information about striped or mirrored volumes, see “Striped Volumes” or “Mirrored Volumes” later in this section.
•Spanned volumes do not provide fault tolerance. If one of the disks containing a spanned volume fails, the entire volume fails, and all data on the spanned volume becomes inaccessible. The reliability for a spanned volume is less than the least reliable disk in the set.
http://technet2.microsoft.com/Windo...79a5-4ba7-ade2-2a8cf5e9ba901033.mspx?mfr=true
500+500+500+500+250+250gb = 2 1/2 terabytes!
