How can I quickly decompress a 1TB (5 million file) 7-Zip (7z) file stored on a NAS

There is a 7-Zip (7z) file (size: 1TB with about 5 million files inside) in a NAS device ruing in iSCSI mode. The 7-Zip file was compressed by the “only store not compress” mode.

When the files are in normal hard disk drive, the compressing speed is so fast(10-20 M/s). But when the 7-Zip (7z) file is in NAS (iSCSI), why the decompressing speed is just less than 1M/s?

Can anyone help that how I can decompress the huge 7-Zip (7z) file on NAS fast (at least reach half speed of compressing)?