Why Is the Linux Block-Level Migration Very Slow?

Symptom

During a Linux block-level migration, you found that the actual migration rate was far lower than the bandwidth limit I have configured.

Possible Causes

The possible causes are as follows:

• A small amount of data is stored in disk blocks.
• A large number of sparse files are stored in source disks.

In a Linux block-level migration, data is compressed before being transmitted. If the disk blocks to be migrated store a small amount of data or are empty, the data compression rate is high, for example, 100 MB of data is compressed to 5 MB. In this case, the displayed migration rate will be very low. But actually, the migration is still performed quickly, and the network connection and bandwidth are normal.