我正在使用Node在VMware下复制文件到SSD,但性能非常低。我运行的基准测试以度量实际速度为:
$ hdparm -tT /dev/sda
/dev/sda:
Timing cached reads: 12004 MB in 1.99 seconds = 6025.64 MB/sec
Timing buffered disk reads: 1370 MB in 3.00 seconds = 456.29 MB/sec
然而,下面这段复制文件的Node代码非常慢,即使连续运行也无法加快速度:
var fs = require("fs");
fs.createReadStream("bigfile").pipe(fs.createWriteStream("tempbigfile"));
然后运行如下:
$ seq 1 10000000 > bigfile
$ ll bigfile -h
-rw-rw-r-- 1 mustafa mustafa 848M Jun 3 03:30 bigfile
$ time node test.js
real 0m4.973s
user 0m2.621s
sys 0m7.236s
$ time node test.js
real 0m5.370s
user 0m2.496s
sys 0m7.190s
这里的问题是什么,如何加快速度?我相信通过调整缓冲区大小可以在C中更快地编写代码。让我困惑的是,当我编写简单的几乎等同于pv的程序,将stdin导入stdout时,速度非常快。process.stdin.pipe(process.stdout);
并且运行结果为:
$ dd if=/dev/zero bs=8M count=128 | pv | dd of=/dev/null
128+0 records in 174MB/s] [ <=> ]
128+0 records out
1073741824 bytes (1.1 GB) copied, 5.78077 s, 186 MB/s
1GB 0:00:05 [ 177MB/s] [ <=> ]
2097152+0 records in
2097152+0 records out
1073741824 bytes (1.1 GB) copied, 5.78131 s, 186 MB/s
$ dd if=/dev/zero bs=8M count=128 | dd of=/dev/null
128+0 records in
128+0 records out
1073741824 bytes (1.1 GB) copied, 5.57005 s, 193 MB/s
2097152+0 records in
2097152+0 records out
1073741824 bytes (1.1 GB) copied, 5.5704 s, 193 MB/s
$ dd if=/dev/zero bs=8M count=128 | node test.js | dd of=/dev/null
128+0 records in
128+0 records out
1073741824 bytes (1.1 GB) copied, 4.61734 s, 233 MB/s
2097152+0 records in
2097152+0 records out
1073741824 bytes (1.1 GB) copied, 4.62766 s, 232 MB/s
$ dd if=/dev/zero bs=8M count=128 | node test.js | dd of=/dev/null
128+0 records in
128+0 records out
1073741824 bytes (1.1 GB) copied, 4.22107 s, 254 MB/s
2097152+0 records in
2097152+0 records out
1073741824 bytes (1.1 GB) copied, 4.23231 s, 254 MB/s
$ dd if=/dev/zero bs=8M count=128 | dd of=/dev/null
128+0 records in
128+0 records out
1073741824 bytes (1.1 GB) copied, 5.70124 s, 188 MB/s
2097152+0 records in
2097152+0 records out
1073741824 bytes (1.1 GB) copied, 5.70144 s, 188 MB/s
$ dd if=/dev/zero bs=8M count=128 | node test.js | dd of=/dev/null
128+0 records in
128+0 records out
1073741824 bytes (1.1 GB) copied, 4.51055 s, 238 MB/s
2097152+0 records in
2097152+0 records out
1073741824 bytes (1.1 GB) copied, 4.52087 s, 238 MB/s