linux下的fastcopy
在拷贝数据的时候，如果遇到一堆小文件，即使总数据量很小，拷贝也会很费时，在win下，有一个软件叫fastcopy，可以实现快速拷贝，据说使用了一种叫内存映射的技术，那么在Linux下有没有呢？
我找了半天，原来LInux下根本不需要单独的软件，用现有的命令组合就OK了！
有高手在两个服务器间传数据，使用命令，实现了快速传送数据。
http://www.4bcj.com/post/2008/01/Fast-File-Copy—Linux!.aspx
All good ideas come out of necessity. We were cloning an instance of
Oracle Financials from one server to another. There are a LOT of files
under < 1k and the copy takes forever. Yesterday the copy was kicked
off using SCP - there was 39GBs to copy over a gigabit switch. This
should have been less than 10 minutes but actually took over 8 hours
because of all the small files. The copy failed and we needed to fix
the problem and copy it a lot faster (30 minutes) today.
After clearing up 10 GBs of log files, we were left with hundreds of
thousands of small files that were going to slow us down. We couldn’t
tarball the file because of a lack of space on the source server. I
started searching around and found this nifty tip that takes our
encryption and streams all the files as one large file:
This requires netcat on both servers.
Destination box: nc -l -p 2342 | tar -C /target/dir -xzf -
Source box: tar -cz /source/dir | nc Target_Box 2342
It’s been about 4 minutes and I’m already 1/3 of the way done!
感谢本校LInux版主ashmer，写了这个shell脚本，可以实现fastcopy, 与诸位共享.
#!/bin/sh
# file: fastcp.sh
source="$1"
target="$2"
if [ "x$1" == "x" ] || [ "x$2" == "x" ] ; then
echo "$0 SOURCE_DIR TARGET_DIR"
exit 1
fi
exec tar -cp "$source" -f - | tar -xpv -C "$target" -f -
#end
PS: 测试了一番，速度竟然由cp的0m21.270s降低至0m6.984s，真是够快的。。。
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一. 文件一次读入速度
linux下读文件这东西最后都是要通过系统调用sys_read(fd,buf,count)来实现的，所以如果要提高速度，就是最简单地调用sys_read的封装，比如直接用read()或fread()。下面是我在linux下的几个测试。
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