SQL Server in raid 10 Vs. RAID 5 performance SQL server I/O subsystem introduction iisqlio test SAN server I/O test tool-sqlioraid5 raid 10 Performance

Raid 10 Vs. RAID 5 performance provides a Performance Data graph that uses sqlio. EXE to generate 8 KB random reads and writes, with a performance gap nearly doubled.

Disk access time = disk seek time + latency

Latency = 1 minute/RPM/2

The main factor determining iops is the array'sAlgorithm, Cache hit rate, and number of disks. The array algorithms vary depending on the array. For example, in hds usp, an ldev (Lun) may have queue or resource restrictions, resulting in a single ldev iops failure. Therefore, when designing the storage I/O, we must use the storage products we use to understand some of the storage's algorithm rules and restrictions.

There is no difference in read iops between RAID5 and raid10. However, for the same business write iops, there is a difference in the iops that eventually falls on the disk, and what we evaluate is the disk iops. If the disk limit is reached, the performance will definitely not go up.

1. Security comparison

In terms of security, there is no doubt that raid10 is more secure than raid5. We can draw this conclusion through simple analysis. When Disk 1 is damaged, raid is invalidated only when the image disk corresponding to disk 1 is damaged. However, for RAID 5, if any of the three remaining disks fails, the raid will fail.

The restoration speed of RAID 10 is also faster than that of RAID 5.

2. Comparison of space utilization

The raid10 utilization rate is 50%, and the RAID5 utilization rate is 75%. The more hard disks, the higher the space utilization of RAID 5.

3. read/write Performance Comparison

The following three operations are analyzed: read, continuous write, and discrete write.

Tip:

The stored cache is described in 2.1.3, because these three operations have a great relationship with the cache.

1) performance differences in read Operations

The number of disks that raid10 can read valid data is 4, and the number of disks that RAID5 can read valid data is also 4 (verification information is distributed on all disks ), therefore, the reading performance of the two should be basically the same.

2) performance differences in continuous writing

In the continuous write operation, if a write cache exists and the algorithm is normal, RAID5 is even better than raid10, although there may not be much difference (here we should assume that there is a certain size of storage, enough write cache, and there is no bottleneck in the CPU for computing and verification ).

This is because the raid check is completed in the cache. For example, for RAID 5 of four disks, you can calculate the check in the memory and write three data and one verification at the same time. Raid10 can only write 2 Data + 2 images at the same time.

3) performance differences in discrete write

For example, if the SQL Server database writes a data block each time, for example, 4 kb or 8 KB, the number of writes is not large and the number of writes is very frequent, therefore, online logs appear to be continuously written. But because it is not guaranteed to be able to fill up a strip of RAID 5, such as 32 KB (ensure that each disk can be written), it is usually more inclined to discrete write (write to the existing data strip ).

4) Comparison of disk iops

RAID5 is preferred for systems with high requirements on space utilization and not particularly high security requirements for large file storage. On the contrary, systems with high security requirements, regardless of the cost, use RAID 10 to write small data volumes frequently.

Based on experience and analysis: raid10 is recommended for small I/O database operations, such as ERP applications. Large file storage and data warehouses, such as Medical PACS and video editing systems, from the perspective of space utilization, RAID5 is recommended.

In an actual case, a standby with a high recovery pressure (mainly writing, but also writing a small Io) adopts the RAID5 solution and finds that the performance is poor, through analysis, the iops of each disk reaches 200 during peak hours, resulting in a very slow response speed. Later it was transformed into raid10 to avoid this performance problem. The iops of each disk was reduced to about 100. Therefore, understanding the principles of RAID 5 and raid 10 is very important for us to design storage I/O based on the characteristics of the application system.

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