如果安装了aspera，prefetch会自动调用。
如果产生如下错误
prefetch -v SRR925811
Maximum file size download limit is 20,971,520KB
2019-06-16T01:54:42 prefetch.2.3.5: Using 'ascp'
2019-06-16T01:54:42 prefetch.2.3.5: Using '/home/kelly/.aspera/connect/bin/ascp'
2019-06-16T01:54:42 prefetch.2.3.5 err: error unexpected while resolving tree within virtual file system module - failed to resolve accession 'SRR925811' - Obsolete software. See https://github.com/ncbi/sra-tools/wiki/Obsolete-software ( 406 )
Redirected!!!
2019-06-16T01:54:43 prefetch.2.3.5 err: name incorrect while evaluating path within network system module - Scheme is 'https'
2019-06-16T01:54:43 prefetch.2.3.5 err: path not found while resolving tree within virtual file system module - 'SRR925811' cannot be found.查看sra-tools版本是否最新版 可以重新安装最新版或建立新的环境安装最新，建议删除。
