RAID technical details 3: soft RAID

In addition to using RAID cards or chips on the motherboard to implement disk arrays, we can directly use software to implement RAID functions in some operating systems, for example, the RAID function is built in Windows 2000/XP.
Before learning about RAID in Windows 2000/XP, let's take a look at Dynamic Disk management, a feature in Windows 2000.
Compared with a basic disk, a dynamic disk no longer uses the previous partitioning method, but is called a volume set. Its role is actually the same as that of a partition, but it has the following differences:
1. You can change the disk capacity at will.
The dynamic disk capacity can be changed without restarting the computer, and data will not be lost, the basic disk will lose all the data if it needs to change the partition capacity (of course, some special disk tool software can change the partition without damaging the data, such as PQMagic ).
2. Disk Space restrictions
A Dynamic Disk can be expanded to a non-sequential disk space. You can also create a cross-disk volume set to combine several disks into a large volume set. The basic disk partition must be the continuous space on the same disk. The maximum partition capacity is of course the disk capacity.
3. Number of volumes or partitions
There is no limit on the number of volumes that a dynamic disk can create on a single disk. The relative basic disk can be divided into up to four zones on a single disk, in addition, DOS or Windows 9X can only be divided into one primary partition and one extended partition.
* Note that dynamic disks can only be used in Windows NT/2000/XP systems. Dynamic disks cannot be identified by other operating systems.
Most users' disks are basic disk types. To use the software RAID function, we must convert them to dynamic disks: Control Panel> Management Tools> Computer Management> disk management, in the View menu, switch one of the windows to the disk list. In this case, you can right-click the menu to convert the selected disk to a dynamic disk.
When dividing dynamic volumes, you can see these types of dynamic volumes.
1. Simple volume: contains the disk space on a single disk, which is the same as the partition function. (When there are two or more dynamic disks in the system and there is no allocated space on both disks, we can select the following two volume separation methods)
2. Cross-zone volume: the cross-zone volume combines unallocated space from multiple disks into one logical volume.
3. Strip volume: Combine multiple (2 to 32) disks with no allocated space to one volume. (If the two dynamic disks in the system share the same capacity, we will see another partition method)
4. Image volume: two identical copies of a single volume, each of which is on a hard disk. RAID 1.
When we have three or more dynamic disks, we can use RAID 5, a more complex RAID method. In this case, a new form of volume splitting appears on the volume splitting interface.
5. RAID 5 volume: equivalent to a zone volume with parity, that is, RAID 5.
For most of the mothers, it is the most economical and practical array format to use the RAID 0, so here we will only explain the construction of the software RAID 0:
To use software RAID 0 in Windows 2000/XP, you must first convert the disk to be included in the array to the Dynamic Disk described above (note that, basic disks and dynamic disks cannot be converted in the default disk management interface of Windows 2000/XP. For details, refer to the description above). Here we try to use partitioning strip, this is exactly the difference between software RAID and RAID chips used to build disk arrays.
We have selected a 29 GB partition to partition the with-area volume. When dividing the with-area volume area, the system will require a corresponding partition, that is to say, other dynamic disks must have the same 29GB or larger unallocated space. After the partition volume is allocated, the two volumes of the same size will be merged by the system, at this time, our formatting and other operations are also performed on both disks.
After building RAID 0, we decided to test its hard disk transfer rate to determine the degree of Performance Improvement for this software RAID. The platform for building software RAID is different from the hardware RAID platform in the previous article, to ensure CPU performance to ensure the implementation of our software RAID, we adopt a high-end system: Athlon XP 1700 +, Samsung 256 mb ddr memory, Asus A7V266-E motherboard, because software RAID has low requirements on hard disk specifications, we choose hard disks of different specifications for the hard disk system.
60 GB and GB of Western data disk.

In the second half of the transmission curve, we can clearly see that the hard disk transfer rate of the software RAID 0 has reached 60 MB/s, completely surpassing the transmission rate of any hard disk in the array, the advantage of RAID 0 began to be reflected. For users pursuing high performance, this should be what they dream.
In Linux, we can also use Raidtools to implement software RAID. This tool can create a variety of disk arrays, such as soft RAID 0, RAID 1, RAID 4, and RAID 5. Before using Raidtools, you must first determine whether the Linux core currently in use supports Md. If you are using 2.0.X and are not compiled by yourself, soft RAID is supported in most cases. If you are not sure, You need to compile the core.
Although RAID can bring us a better speed experience and data security, it should be noted that most of the current market's cheap IDE-RAID solutions are essentially "semi-soft" RAID, only RAID control information is integrated into the RAID chip, so the CPU usage is relatively high and the performance is not very stable. This is also because the performance of software RAID 0 in high-end systems can sometimes exceed the "hardware" RAID
0.
For users, high-performance IDE-RAID storage systems, or the need for strong CPU computing capabilities, or more expensive RAID card, so disk arrays should still be considered relatively high-end applications. However, for novice users, it is also a good choice to use simple and inexpensive disk arrays to improve the availability of computer data or increase the storage speed. Of course, its performance is far from comparable to that of high-end systems.
In short, we see more and more RAID architecture in the market, especially in the low-end market, more and more popular cheap IDE-RAID solutions and hard disk prices continue to decline to take care of each other, it seems that the future trend of personal data storage is also predicted. Let's wait and see.