Comparison between raid1 and RAID5

Io performance: In read operations, raid10 and RAID5 are equivalent. Raid-5 performs write operations on small data (such as small data smaller than each band) two reads, two writes, and two XOR operations are required. For a single user's write operation, the old data must be removed from the verification disk before the new data application, the entire execution process is as follows: Read the old data, perform XOR between the old data and the new data, create an immediate value, and read the verification information of the old data, perform XOR on the Real-Time Value and verification data, and write new verification information. To reduce the impact on the system, most RAID5 reads and writes the entire strip (including verification strip) to the cache, and performs two XOR operations, then, the system sends out parallel write operations (usually the entire band). Even with the above optimization, the system still needs to perform additional read and XOR operations for this write operation. The difficulty of a small write operation makes raid-5 rarely used in intensive write operations, such as rollback fields and redo logs. Of course, you can also define the band size of the storage system as the data size of regular read/write operations to match, but this will limit the flexibility of the system and will not apply to other applications in the enterprise.

For raid10, since there is no data verification, each write operation only performs a write operation. In terms of Write Performance, raid 10 is better than RAID 5.

Data Reconstruction:

For raid 10, when a disk fails, the data reconstruction operation only copies a new disk. If the disk capacity is assumed to be 250 GB, the copied data volume is 250 GB.

For the RAID5 storage array, you need to read data from each disk and recalculate the data volume of a hard disk. If RAID5 is created in 4 + 1 mode, the capacity of each disk is also 250 GB. Therefore, you need to read a total of GB of data from the remaining four disks to calculate the data size of GB.

From this point of view, the workload and time spent on Data Reconstruction of RAID5 should be much higher than that of raid10, and the load change will affect the performance during the reconstruction, A long time means that the possibility of data corruption becomes greater.

Data security protection:

If a disk in raid10 is invalid, data loss occurs only when the corresponding image disk of the disk fails. No data loss occurs when other disks become invalid.

If a disk in RAID5 is invalid, any failure of the disk will cause data loss.

In summary, raid10 and RAID5 will take longer than raid10 to reconstruct Data after a disk becomes invalid, at the same time, the system load on RAID5 is higher than that on raid10 during reconstruction, and the possibility of data loss on RAID5 is higher than that on raid10. Therefore, during data reconstruction, the reliability of the RAID5 system is far lower than that on raid10.

RAID5 has a higher disk space usage rate than raid10, RAID5 has a (N-1)/n (n is the number of disks in the array), and raid10 has only 50% disk space utilization.

However, considering the disk, the quality of ATA or SATA hard disks produced by hard disk manufacturers can already be used for enterprise-level applications, and the increase in capacity is quite large, the storage capacity of a single disk is GB. Small-diameter disks are used for high-speed SCSI hard disks, resulting in a relatively slow increase in capacity. The cost of ATA disks is much lower than that of SCSI disks.

Therefore, in a storage system that uses expensive FC or SCSI hard disks, RAID5 can be used to compromise the situation where the budget is limited and the data security requirements are not high; other applications use a large-capacity ATA or SATA hard disk combined with raid 10, which not only reduces the cost of RAID 10 to get a certain amount of storage space, but also requires double the cost of ownership of the disk space, this avoids the disadvantages of RAID 5 compared with raid 10.

In enterprise applications, combining raid 10 with Sata disks means a better choice.