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After the SmartThin function is enabled, the storage system creates thin LUNs and does not allocate the configured capacity to LUNs at a time. In the LUN capacity range, the storage system dynamically allocates storage resources based on the actual capacity of the host to implement on-demand allocation. Compared with thick LUN, there are differences in read/write performance.
The actual difference between thin LUN and thick LUN is the mapping between LBA and PBA,
1. If the LBA and PBA are in one-to-one correspondence, then it is thick LUN LBA-Logical block address
2. If the LBA and PBA do not correspond to each other, then thin LUN PBA-Physical block address.
Write performance
· For the first time: The thick LUN is formatted after the LUN is created. Therefore, only the write operation on the host I/O is involved. When new data is written into the thin LUN, space is allocated to the, which brings more data to the I/O. The write process is longer and imposes additional pressure on the back-end hard disk. In this case, the performance of the thick LUN is better than that of the thin LUN.
· Overwritten write: Because both thin LUN and thick LUN have completed the allocation of the write space, no extra overhead is generated. In this case, the performance of the two is equivalent.
Read performance
· Sequential reading: The thin LUN dynamically allocates storage resources based on the actual requirements of users. The space allocation has discontinuous time and therefore affects the space continuity that maps to disks. When the thick LUN is created, the system allocates storage resources to the storage resources at a time through the automatic resource configuration technology. This ensures the space continuity of the mapping to the disk. The sequential read efficiency of mechanical disks is higher. Therefore, thick LUN performance is better than thin LUN in sequential read mode.
· Random reading: Because the address space accessed during random read is discrete, the performance of the two is equivalent.
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