生成实验数据
mkdir {
0..9}{
a..z}
for i in *;do
cd $i
echo $RANDOM > $RANDOM
cd ..
done
打包时间对比
- cpio
$ time find . | cpio -o > bnk.cpio real 0m0.094s user 0m0.012s sys 0m0.012s $ mv bnk.cpio ../ - tar
$ time tar cf bnk.tar { 0..9}{ a..z} real 0m0.208s user 0m0.013s sys 0m0.032s $ mv bnk.tar ../
cpio 打包速度较 tar 快一倍以上。
文件大小对比与十六进制分析
$ du bnk*
40 bnk.cpio
400 bnk.tar
- cpio
$ hexdump -C bnk.cpio | less 00000000 c7 71 02 08 17 8f ed 41 e8 03 e8 03 06 01 00 00 |.q.....A........| 00000010 90 66 6b fd 02 00 00 00 00 00 2e 00 c7 71 02 08 |.fk..........q..| 00000020 9b 09 ed 41 e8 03 e8 03 02 00 00 00 90 66 9d fc |...A.........f..| 00000030 03 00 00 00 00 00 30 61 00 00 c7 71 02 08 53 57 |......0a...q..SW| 00000040 a4 81 e8 03 e8 03 01 00 00 00 90 66 9d fc 08 00 |...........f....| 00000050 00 00 05 00 30 61 2f 33 32 39 32 00 31 34 31 38 |....0a/3292.1418| 00000060 0a 00 c7 71 02 08 03 80 ed 41 e8 03 e8 03 02 00 |...q.....A......| 00000070 00 00 90 66 9d fc 03 00 00 00 00 00 30 62 00 00 |...f........0b..| 00000080 c7 71 02 08 77 89 a4 81 e8 03 e8 03 01 00 00 00 |.q..w...........| 00000090 90 66 9d fc 09 00 00 00 05 00 30 62 2f 32 32 31 |.f........0b/221| 000000a0 35 38 00 00 36 37 32 37 0a 00 c7 71 02 08 27 14 |58..6727...q..'.| 000000b0 ed 41 e8 03 e8 03 02 00 00 00 90 66 9d fc 03 00 |.A.........f....| 000000c0 00 00 00 00 30 63 00 00 c7 71 02 08 d4 17 a4 81 |....0c...q......| 000000d0 e8 03 e8 03 01 00 00 00 90 66 9d fc 09 00 00 00 |.........f......| 000000e0 06 00 30 63 2f 31 39 32 32 33 00 00 33 30 31 34 |..0c/19223..3014| 000000f0 32 0a c7 71 02 08 b4 f6 ed 41 e8 03 e8 03 02 00 |2..q.....A......| 00000100 00 00 90 66 9d fc 03 00 00 00 00 00 30 64 00 00 |...f........0d..| 00000110 c7 71 02 08 9b 7b a4 81 e8 03 e8 03 01 00 00 00 |.q...{ ..........| 00000120 90 66 9d fc 09 00 00 00 05 00 30 64 2f 32 34 34 |.f........0d/244| 00000130 33 31 00 00 34 38 32 32 0a 00 c7 71 02 08 6a 34 |31..4822...q..j4| 00000140 ed 41 e8 03 e8 03 02 00 00 00 90 66 9d fc 03 00 |.A.........f....| 00000150 00 00 00 00 30 65 00 00 c7 71 02 08 55 57 a4 81 |....0e...q..UW..| 00000160 e8 03 e8 03 01 00 00 00 90 66 9d fc 08 00 00 00 |.........f......| 00000170 06 00 30 65 2f 31 38 36 32 00 31 38 32 35 37 0a |..0e/1862.18257.| 00000180 c7 71 02 08 04 80 ed 41 e8 03 e8 03 02 00 00 00 |.q.....A........| 00000190 90 66 9d fc 03 00 00 00 00 00 30 66 00 00 c7 71 |.f........0f...q| 000001a0 02 08 78 89 a4 81 e8 03 e8 03 01 00 00 00 90 66 |..x............f| 000001b0 9d fc 09 00 00 00 06 00 30 66 2f 32 39 33 33 34 |........0f/29334| 000001c0 00 00 31 35 34 39 31 0a c7 71 02 08 04 16 ed 41 |..15491..q.....A| - bnk
$ hexdump -C bnk.tar | less 00000000 30 61 2f 00 00 00 00 00 00 00 00 00 00 00 00 00 |0a/.............| 00000010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 00000060 00 00 00 00 30 30 30 30 37 35 35 00 30 30 30 31 |....0000755.0001| 00000070 37 35 30 00 30 30 30 31 37 35 30 00 30 30 30 30 |750.0001750.0000| 00000080 30 30 30 30 30 30 30 00 31 34 36 34 34 31 37 36 |0000000.14644176| 00000090 32 33 35 00 30 31 30 36 37 34 00 20 35 00 00 00 |235.010674. 5...| 000000a0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 00000100 00 75 73 74 61 72 20 20 00 61 64 61 6d 6c 7a 00 |.ustar .adamlz.| 00000110 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| 00000120 00 00 00 00 00 00 00 00 00 61 64 61 6d 6c 7a 00 |.........adamlz.| 00000130 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 00000200 30 61 2f 33 32 39 32 00 00 00 00 00 00 00 00 00 |0a/3292.........| 00000210 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 00000260 00 00 00 00 30 30 30 30 36 34 34 00 30 30 30 31 |....0000644.0001| 00000270 37 35 30 00 30 30 30 31 37 35 30 00 30 30 30 30 |750.0001750.0000| 00000280 30 30 30 30 30 30 35 00 31 34 36 34 34 31 37 36 |0000005.14644176| 00000290 32 33 35 00 30 31 31 32 31 31 00 20 30 00 00 00 |235.011211. 0...| 000002a0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 00000300 00 75 73 74 61 72 20 20 00 61 64 61 6d 6c 7a 00 |.ustar .adamlz.| 00000310 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| 00000320 00 00 00 00 00 00 00 00 00 61 64 61 6d 6c 7a 00 |.........adamlz.| 00000330 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 00000400 31 34 31 38 0a 00 00 00 00 00 00 00 00 00 00 00 |1418............| 00000410 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
可见 cpio 比 tar 小得多，cpio 通过文本保存目录及文件信息，无索引，而 tar 通过地址结构分别保存目录、文件及文件归属。这里注意，tar 文件大小限制取决于文件系统，而 cpio 最大仅支持 4GiB。
解包时间对比
- cpio
$ time cpio -id < bnk.cpio real 0m0.193s user 0m0.003s sys 0m0.050s - bnk
$ time tar xf bnk.tar real 0m0.031s user 0m0.002s sys 0m0.014s
在解包速度上，tar 比 cpio 更快。
结论
| 打包耗时 | 解包耗时 | 文件大小 | 备注 | |
|---|---|---|---|---|
| cpio | 1 | 6.22 | 1 | 无索引，最大仅支持 4GiB |
| tar | 2.21 | 1 | 10 | 地址索引，大小极限取决于文件系统 |
非必要场景下，更推荐使用 tar 打包备份。
