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2010-06-20 01:28:21
基于Dedup的数据打包技术
作者简介 ：刘爱贵，研究方向为网络存储、数据挖掘和分布式计算；毕业于中科院，目前从事存储软件研发工作。 Email:
Aigui.Liu@gmail.com
注： 作者学识和经验水平有限，如有错误或不当之处，敬请批评指正。
0、引言
Tar, winrar,
winzip是最为常见的数据打包工具软件，它们把文件集体封装成一个单独的数据包，从而方便数据的分布、传输、归档以及持久保存等目的。这类工具通常都
支持数据压缩技术，从而有效减少数据的存储空间，常用压缩算法有Huffman编码、Z77/z78、LZW等。压缩算法的原理是通过对数据的重新编码，
高频率数据片段采用较短的编码，低频率数据片段采用较长的编码，从而获得全局的上数据量较小的文件表示。
1、Dedup原理
Deduplication，即重复数据删除，它是一种非常新的且流行度很高的存储技术，可以大大减少数据的数量。重复数据删除技术，通过数据集中重复的
数据，从而消除冗余数据。借助dedup技术，可以提高存储系统的效率，有效节约成本、减少传输过程中的网络带宽。同时它也是一种绿色存储技术，能有效降
低能耗(存储空间小了，所需要存储系统磁盘也就少了，自然所需要电能就减少了)。
dedup按照消重的粒度可以分为文件级和数据块级。文件级的dedup技术也称为单一实例存储(SIS, Single Instance
Store)，数据块级的重复数据删除，其消重粒度更小，可以达到4-24KB之间。显然，数据块级的可以提供更高的数据消重率，因此目前主流的
dedup产品都是数据块级的。重复数据删除原理如下图所示。将文件都分割成数据块(可以是定长或变长的数据块)，采用MD5或SHA1等Hash算法
(可以同时使用两种或以上hash算法，或CRC校验等，以获得非常小概率的数据碰撞发生)为数据块计算FingerPrint。具有相同FP指纹的数据
块即可认为是相同的数据块，存储系统中仅需要保留一份。这样，一个物理文件在存储系统中就对应一个逻辑表示，由一组FP组成的元数据。当进行读取文件时，
先读取逻辑文件，然后根据FP序列，从存储系统中取出相应数据块，还原物理文件副本。
重复数据删除目前主要应用于数据备份，因此对数据进行多次备份后，存在大量重复数据，非常适合dedup技术。事实上，dedup技术可以用于很多场合，
包括在线数据、近线数据、离线数据存储系统，甚至可以在文件系统、卷管理器、NAS、SAN中实施。还可以用于网络数据传输，当然也可以应用于数据打包技
术。dedup技术可以帮助众多应用降低数据存储量，节省网络带宽，提高存储效率、减小备份窗口，绿色节能。这里，基于dedup实现一种数据打包技术。
2、基于Dedup的数据打包模型
数据包文件的数据布局：
|
Header |
Unique block data |
File metadata |
数据包由三部分组成：文件头(header)、唯一数据块集(unique block data)和逻辑文件元数据(file metadata)。其中，header为一个结构体，定义了数据块大小、唯一数据块数量、数据块ID大小、包中文件数量、元数据在包中的位置等元信息。 文件头后紧接就存储着所有唯一的数据块，大小和数量由文件头中元信息指示。在数据块之后，就是数据包中文件的逻辑表示元数据，由多个实体组成，结构如下所 示，一个实体表示一个文件。解包时根据文件的元数据，逐一提取数据块，还原出当初的物理文件。
逻辑文件的元数据表示：
|
Entry header |
pathname |
Entry data |
Last block data |
逻辑文件的实体头中记录着文件名长度、数据块数量、数据块ID大小和最后一个数据块大小等信息。紧接着是文件名数据，长度在实体头中定义。文件
名数据之后，存储着一组唯一数据块的编号，编号与唯一数据块集中的数据块一一对应。最后存储着文件最后一个数据块，由于这个数据块大小通常比正常数据块
小，重复概率非常小，因此单独保存。
3、原型实现
基于上面的数据布局，就可以实现支持重复数据删除的数据打包方法。本人在Linux系统上实现了一个原型，实现中使用了hashtable来记录和查询唯
一数据块信息，使用MD5算法计算数据块指纹，并使用zlib中的z77压缩算法对删除了重复数据后的数据包进行压缩。hashtable, MD5,
z77算法和实现，这里不作介绍，有兴趣的读者可以参考相关资源。下面给出dedup.h, dedup.c
undedup.c源码文件。目前实现的原型还相对比较粗糙。
/* dedup.h */
#ifndef _DEDUP_H
#define _DEDUP_H
#include "md5.h"
#include "hash.h"
#include "hashtable.h"
#include "libz.h"
#ifdef __cplusplus
extern "C" {
#endif
/*
* deduplication file data layout
* --------------------------------------------------
* | header | unique block data | file metadata |
* --------------------------------------------------
*
* file metedata entry layout
* -----------------------------------------------------------------
* | entry header | pathname | entry data | last block data |
* -----------------------------------------------------------------
*/
typedef unsigned int block_id_t;
#define BLOCK_SIZE 4096 /* 4K Bytes */
#define BACKET_SIZE 10240
#define MAX_PATH_LEN 255
#define BLOCK_ID_SIZE (sizeof(block_id_t))
/* deduplication package header */
#define DEDUP_MAGIC_NUM 0x1329149
typedef struct _dedup_package_header {
unsigned int block_size;
unsigned int block_num;
unsigned int blockid_size;
unsigned int magic_num;
unsigned int file_num;
unsigned long long metadata_offset;
} dedup_package_header;
#define DEDUP_PKGHDR_SIZE (sizeof(dedup_package_header))
/* deduplication metadata entry header */
typedef struct _dedup_entry_header {
unsigned int path_len;
unsigned int block_num;
unsigned int entry_size;
unsigned int last_block_size;
int mode;
} dedup_entry_header;
#define DEDUP_ENTRYHDR_SIZE (sizeof(dedup_entry_header))
#ifdef __cplusplus
}
#endif
#endif
/* dedup.c */
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include "dedup.h"
/* unique block number in package */
static unsigned int g_unique_block_nr = 0;
/* regular file number in package */
static unsigned int g_regular_file_nr = 0;
/* block length */
static unsigned int g_block_size = BLOCK_SIZE;
/* hashtable backet number */
static unsigned int g_htab_backet_nr = BACKET_SIZE;
void show_md5(unsigned char md5_checksum[16])
{
int i;
for (i = 0; i < 16; i++)
{
printf("%02x", md5_checksum[i]);
}
}
void show_pkg_header(dedup_package_header dedup_pkg_hdr)
{
printf("block_size = %d\n", dedup_pkg_hdr.block_size);
printf("block_num = %d\n", dedup_pkg_hdr.block_num);
printf("blockid_size = %d\n", dedup_pkg_hdr.blockid_size);
printf("magic_num = 0x%x\n", dedup_pkg_hdr.magic_num);
printf("file_num = %d\n", dedup_pkg_hdr.file_num);
printf("metadata_offset = %lld\n", dedup_pkg_hdr.metadata_offset);
}
int dedup_regfile(char *fullpath, int prepos, int fd_bdata, int fd_mdata, hashtable *htable, int debug)
{
int fd;
char *buf = NULL;
unsigned int rwsize, pos;
unsigned char md5_checksum[16 + 1] = {0};
unsigned int *metadata = NULL;
unsigned int block_num = 0;
struct stat statbuf;
dedup_entry_header dedup_entry_hdr;
if (-1 == (fd = open(fullpath, O_RDONLY)))
{
perror("open regulae file");
return errno;
}
if (-1 == fstat(fd, &statbuf))
{
perror("fstat regular file");
goto _DEDUP_REGFILE_EXIT;
}
block_num = statbuf.st_size / g_block_size;
metadata = (unsigned int *)malloc(BLOCK_ID_SIZE * block_num);
if (metadata == NULL)
{
perror("malloc metadata for regfile");
goto _DEDUP_REGFILE_EXIT;
}
buf = (char *)malloc(g_block_size);
if (buf == NULL)
{
perror("malloc buf for regfile");
goto _DEDUP_REGFILE_EXIT;
}
pos = 0;
while (rwsize = read(fd, buf, g_block_size))
{
/* if the last block */
if (rwsize != g_block_size)
break;
/* calculate md5 */
md5(buf, rwsize, md5_checksum);
/* check hashtable with hashkey */
unsigned int *bindex = (block_id_t *)hash_value((void *)md5_checksum, htable);
if (bindex == NULL)
{
bindex = (unsigned int *)malloc(BLOCK_ID_SIZE);
if (NULL == bindex)
{
perror("malloc in dedup_regfile");
break;
}
/* insert hash entry and write unique block into bdata*/
*bindex = g_unique_block_nr;
hash_insert((void *)strdup(md5_checksum), (void *)bindex, htable);
write(fd_bdata, buf, rwsize);
g_unique_block_nr++;
}
metadata[pos] = *bindex;
memset(buf, 0, g_block_size);
memset(md5_checksum, 0, 16 + 1);
pos++;
}
/* write metadata into mdata */
dedup_entry_hdr.path_len = strlen(fullpath) - prepos;
dedup_entry_hdr.block_num = block_num;
dedup_entry_hdr.entry_size = BLOCK_ID_SIZE;
dedup_entry_hdr.last_block_size = rwsize;
dedup_entry_hdr.mode = statbuf.st_mode;
write(fd_mdata, &dedup_entry_hdr, sizeof(dedup_entry_header));
write(fd_mdata, fullpath + prepos, dedup_entry_hdr.path_len);
write(fd_mdata, metadata, BLOCK_ID_SIZE * block_num);
write(fd_mdata, buf, rwsize);
g_regular_file_nr++;
_DEDUP_REGFILE_EXIT:
close(fd);
if (metadata) free(metadata);
if (buf) free(buf);
return 0;
}
int dedup_dir(char *fullpath, int prepos, int fd_bdata, int fd_mdata, hashtable *htable, int debug)
{
DIR *dp;
struct dirent *dirp;
struct stat statbuf;
char subpath[MAX_PATH_LEN] = {0};
if (NULL == (dp = opendir(fullpath)))
{
return errno;
}
while ((dirp = readdir(dp)) != NULL)
{
if (strcmp(dirp->d_name, ".") == 0 || strcmp(dirp->d_name, "..") == 0)
continue;
sprintf(subpath, "%s/%s", fullpath, dirp->d_name);
if (0 == lstat(subpath, &statbuf))
{
if (debug)
printf("%s\n", subpath);
if (S_ISREG(statbuf.st_mode))
dedup_regfile(subpath, prepos, fd_bdata, fd_mdata, htable,debug);
else if (S_ISDIR(statbuf.st_mode))
dedup_dir(subpath, prepos, fd_bdata, fd_mdata, htable, debug);
}
}
closedir(dp);
return 0;
}
int dedup_package(int path_nr, char **src_paths, char *dest_file, int debug)
{
int fd, fd_bdata, fd_mdata, ret = 0;
struct stat statbuf;
hashtable *htable = NULL;
dedup_package_header dedup_pkg_hdr;
char **paths = src_paths;
int i, rwsize, prepos;
char buf[1024 * 1024] = {0};
if (-1 == (fd = open(dest_file, O_WRONLY | O_CREAT, 0755)))
{
perror("open dest file");
ret = errno;
goto _DEDUP_PKG_EXIT;
}
htable = create_hashtable(g_htab_backet_nr);
if (NULL == htable)
{
perror("create_hashtable");
ret = errno;
goto _DEDUP_PKG_EXIT;
}
fd_bdata = open("./.bdata", O_RDWR | O_CREAT, 0777);
fd_mdata = open("./.mdata", O_RDWR | O_CREAT, 0777);
if (-1 == fd_bdata || -1 == fd_mdata)
{
perror("open bdata or mdata");
ret = errno;
goto _DEDUP_PKG_EXIT;
}
g_unique_block_nr = 0;
g_regular_file_nr = 0;
for (i = 0; i < path_nr; i++)
{
if (lstat(paths[i], &statbuf) < 0)
{
perror("lstat source path");
ret = errno;
goto _DEDUP_PKG_EXIT;
}
if (S_ISREG(statbuf.st_mode) || S_ISDIR(statbuf.st_mode))
{
if (debug)
printf("%s\n", paths[i]);
/* get filename position in pathname */
prepos = strlen(paths[i]) - 1;
if (strcmp(paths[i], "/") != 0 && *(paths[i] + prepos) == '/')
{
*(paths[i] + prepos--) = '\0';
}
while(*(paths[i] + prepos) != '/' && prepos >= 0) prepos--;
prepos++;
if (S_ISREG(statbuf.st_mode))
dedup_regfile(paths[i], prepos, fd_bdata, fd_mdata, htable, debug);
else
dedup_dir(paths[i], prepos, fd_bdata, fd_mdata, htable, debug);
}
else
{
if (debug)
printf("%s is not regular file or directory.\n", paths[i]);
}
}
/* fill up dedup package header */
dedup_pkg_hdr.block_size = g_block_size;
dedup_pkg_hdr.block_num = g_unique_block_nr;
dedup_pkg_hdr.blockid_size = BLOCK_ID_SIZE;
dedup_pkg_hdr.magic_num = DEDUP_MAGIC_NUM;
dedup_pkg_hdr.file_num = g_regular_file_nr;
dedup_pkg_hdr.metadata_offset = DEDUP_PKGHDR_SIZE + g_block_size * g_unique_block_nr;
write(fd, &dedup_pkg_hdr, DEDUP_PKGHDR_SIZE);
/* fill up dedup package unique blocks*/
lseek(fd_bdata, 0, SEEK_SET);
while(rwsize = read(fd_bdata, buf, 1024 * 1024))
{
write(fd, buf, rwsize);
memset(buf, 0, 1024 * 1024);
}
/* fill up dedup package metadata */
lseek(fd_mdata, 0, SEEK_SET);
while(rwsize = read(fd_mdata, buf, 1024 * 1024))
{
write(fd, buf, rwsize);
memset(buf, 0, 1024 * 1024);
}
if (debug)
show_pkg_header(dedup_pkg_hdr);
_DEDUP_PKG_EXIT:
close(fd);
close(fd_bdata);
close(fd_mdata);
unlink("./.bdata");
unlink("./.mdata");
hash_free(htable);
return ret;
}
void usage()
{
printf("Usage: dedup [OPTION...]
printf("\nPackage files with deduplicaton technique.\n");
printf("Mandatory arguments to long options are mandatory for short options too.\n");
printf(" -z, --compress filter the archive through compress\n");
printf(" -b, --block block size for deduplication, default is 4096\n");
printf(" -t, --hashtable hashtable backet number, default is 10240\n");
printf(" -d, --debug print debug messages\n");
printf(" -h, --help give this help list\n");
printf("\nReport bugs to
}
int main(int argc, char *argv[])
{
char tmp_file[] = "./.dedup\0";
int bz = 0, bhelp = 0, bdebug = 0;
int ret = -1, c;
struct option longopts[] =
{
{"compress", 0, &bz, 'z'},
{"block", 1, 0, 'b'},
{"hashtable", 1, 0, 't'},
{"debug", 0, &bdebug, 'd'},
{"help", 0, &bhelp, 'h'},
{0, 0, 0, 0}
};
/* parse options */
while ((c = getopt_long (argc, argv, "zb:t:dh", longopts, NULL)) != EOF)
{
switch(c)
{
case 'z':
bz = 1;
break;
case 'b':
g_block_size = atoi(optarg);
break;
case 't':
g_htab_backet_nr = atoi(optarg);
break;
case 'd':
bdebug = 1;
break;
case 'h':
case '?':
default:
bhelp = 1;
break;
}
}
if (bhelp == 1 || (argc - optind) < 2)
{
usage();
return 0;
}
if (bz)
{
/* dedup and compress */
ret = dedup_package(argc - optind -1 , argv + optind + 1, tmp_file, bdebug);
if (ret == 0)
{
ret = zlib_compress_file(tmp_file, argv[optind]);
unlink(tmp_file);
}
}
else
{
/* dedup only */
ret = dedup_package(argc - optind - 1, argv + optind + 1, argv[optind], bdebug);
}
return ret;
}
/* undedup.c */
#include
#include
#include
#include
#include
#include
#include
#include
#include "dedup.h"
/* block length */
static unsigned int g_block_size = BLOCK_SIZE;
void show_pkg_header(dedup_package_header dedup_pkg_hdr)
{
printf("block_size = %d\n", dedup_pkg_hdr.block_size);
printf("block_num = %d\n", dedup_pkg_hdr.block_num);
printf("blockid_size = %d\n", dedup_pkg_hdr.blockid_size);
printf("magic_num = 0x%x\n", dedup_pkg_hdr.magic_num);
printf("file_num = %d\n", dedup_pkg_hdr.file_num);
printf("metadata_offset = %lld\n", dedup_pkg_hdr.metadata_offset);
}
int prepare_target_file(char *pathname, char *basepath, int mode)
{
char fullpath[MAX_PATH_LEN] = {0};
char path[MAX_PATH_LEN] = {0};
char *p = NULL;
int pos = 0, fd;
sprintf(fullpath, "%s/%s", basepath, pathname);
p = fullpath;
while (*p != '\0')
{
path[pos++] = *p;
if (*p == '/')
mkdir(path, 0755);
p++;
}
fd = open(fullpath, O_WRONLY | O_CREAT, mode);
return fd;
}
int undedup_regfile(int fd, dedup_entry_header dedup_entry_hdr, char *dest_dir, int debug)
{
char pathname[MAX_PATH_LEN] = {0};
block_id_t *metadata = NULL;
unsigned int block_num = 0;
char *buf = NULL;
char *last_block_buf = NULL;
long long offset, i;
int fd_dest, ret = 0;
metadata = (block_id_t *) malloc(BLOCK_ID_SIZE * dedup_entry_hdr.block_num);
if (NULL == metadata)
return errno;
buf = (char *)malloc(g_block_size);
last_block_buf = (char *)malloc(g_block_size);
if (NULL == buf || NULL == last_block_buf)
{
ret = errno;
goto _UNDEDUP_REGFILE_EXIT;
}
read(fd, pathname, dedup_entry_hdr.path_len);
read(fd, metadata, BLOCK_ID_SIZE * dedup_entry_hdr.block_num);
read(fd, last_block_buf, dedup_entry_hdr.last_block_size);
fd_dest = prepare_target_file(pathname, dest_dir, dedup_entry_hdr.mode);
if (fd_dest == -1)
{
ret = errno;
goto _UNDEDUP_REGFILE_EXIT;
}
if (debug)
printf("%s/%s\n", dest_dir, pathname);
/* write regular block */
block_num = dedup_entry_hdr.block_num;
for(i = 0; i < block_num; ++i)
{
offset = DEDUP_PKGHDR_SIZE + metadata[i] * g_block_size;
lseek(fd, offset, SEEK_SET);
read(fd, buf, g_block_size);
write(fd_dest, buf, g_block_size);
}
/* write last block */
write(fd_dest, last_block_buf, dedup_entry_hdr.last_block_size);
close(fd_dest);
_UNDEDUP_REGFILE_EXIT:
if (metadata) free(metadata);
if (buf) free(buf);
if (last_block_buf) free(last_block_buf);
return ret;
}
int undedup_package(char *src_file, char *dest_dir, int debug)
{
int fd, i, ret = 0;
dedup_package_header dedup_pkg_hdr;
dedup_entry_header dedup_entry_hdr;
unsigned long long offset;
if (-1 == (fd = open(src_file, O_RDONLY)))
{
perror("open source file");
return errno;
}
if (read(fd, &dedup_pkg_hdr, DEDUP_PKGHDR_SIZE) != DEDUP_PKGHDR_SIZE)
{
perror("read dedup_package_header");
ret = errno;
goto _UNDEDUP_PKG_EXIT;
}
if (debug)
show_pkg_header(dedup_pkg_hdr);
offset = dedup_pkg_hdr.metadata_offset;
for (i = 0; i < dedup_pkg_hdr.file_num; ++i)
{
if (lseek(fd, offset, SEEK_SET) == -1)
{
ret = errno;
break;
}
if (read(fd, &dedup_entry_hdr, DEDUP_ENTRYHDR_SIZE) != DEDUP_ENTRYHDR_SIZE)
{
ret = errno;
break;
}
ret = undedup_regfile(fd, dedup_entry_hdr, dest_dir, debug);
if (ret != 0)
break;
offset += DEDUP_ENTRYHDR_SIZE;
offset += dedup_entry_hdr.path_len;
offset += dedup_entry_hdr.block_num * dedup_entry_hdr.entry_size;
offset += dedup_entry_hdr.last_block_size;
}
_UNDEDUP_PKG_EXIT:
close(fd);
return ret;
}
void usage()
{
printf("Usage: undedup [OPTION...]
printf("\nUnpackage files with deduplicaton technique.\n");
printf("Mandatory arguments to long options are mandatory for short options too.\n");
printf(" -z, --uncompress filter the archive through uncompress\n");
printf(" -c, --directory change to directory, default is PWD\n");
printf(" -d, --debug print debug messages\n");
printf(" -h, --help give this help list\n");
printf("\nReport bugs to
}
int main(int argc, char *argv[])
{
char tmp_file[] = "./.dedup\0";
char path[MAX_PATH_LEN] = ".\0";
int bz = 0, bhelp = 0, bdebug = 0;
int ret = -1, c;
struct option longopts[] =
{
{"compress", 0, &bz, 'z'},
{"directory", 1, 0, 'c'},
{"debug", 0, &bdebug, 'd'},
{"help", 0, &bhelp, 'h'},
{0, 0, 0, 0}
};
while ((c = getopt_long (argc, argv, "zc:dh", longopts, NULL)) != EOF)
{
switch(c)
{
case 'z':
bz = 1;
break;
case 'c':
sprintf(path, "%s", optarg);
break;
case 'd':
bdebug = 1;
break;
case 'h':
case '?':
default:
bhelp = 1;
break;
}
}
if (bhelp == 1 || (argc - optind) < 1)
{
usage();
return 0;
}
if (bz)
{
/* uncompress and undedup */
ret = zlib_decompress_file(argv[optind], tmp_file);
if (ret == 0)
{
ret = undedup_package(tmp_file, path, bdebug);
unlink(tmp_file);
}
}
else
{
/* only undedup */
ret = undedup_package(argv[optind], path, bdebug);
}
return ret;
}
/* dedup usage */
Usage: dedup [OPTION...]
Package files with deduplicaton technique.
-z, --compress filter the archive through compress
-b, --block block size for deduplication, default is 4096
-t, --hashtable hashtable backet number, default is 10240
-d, --debug print debug messages
-h, --help give this help list
/* undedup usage */
Usage: undedup [OPTION...]
Unpackage files with deduplicaton technique.
-z, --uncompress filter the archive through uncompress
-c, --directory change to directory, default is PWD
-d, --debug print debug messages
-h, --help give this help list
4、初步测试
这里使用linux最新的kernel源码进行测试，并与tar工具进行比较。从
下载linux-2.6.32.tar.gz文件，并解压出源文件，然后分别使用tar和dedup工具进行打包，分别得到以下几个文件。
|
Filename |
File size |
commands |
|
linux-2.2.6.32.tar |
382392320 (365MB) |
tar cvf linux-2.6.32.tar linux-2.6.32/ |
|
linux-2.2.6.32.tar.dd |
380381944 (363M) |
dedup linux-2.6.32.tar.dd linux-2.6.32.tar |
|
linux-2.2.6.32.dd |
357325910 (341MB) |
dedup linux-2.6.32.dd linux-2.6.32/ |
|
linux-2.2.6.32.tar.gz |
84322110 (81MB) |
gzip -c linux-2.6.32.tar > linux-2.6.32.tar.gz |
|
linux-2.2.6.32.tar.dd.gz |
83978234 (81MB) |
gzip -c linux-2.6.32.tar.dd > linux-2.6.32.tar.dd.gz |
|
linux-2.2.6.32.dd.gz |
83674306 (80MB) |
gzip -c linux-2.6.32.dd > linux-2.6.32.dd.gz |
linux-2.6.32.tar.gz解压出来的kernel源码文件数据很多，使用这个文件来测试应该具有普遍的意义。通过初步的测试结果，我们可以
看出，即使在这样不明确数据是否具备较高重复率的情况下，dedup技术也能较明显地减少数据包的数据量。在数据重复率很高的测试用例下，比如全0或全1
的大文件，dedup要远远优于tar。比如，全0的64MB文件，tar+gzip的结果为65KB，而dedup的结果才有286字节。
5、TODO
1、变长数据块。目前是定长数据块的实现，技术上较为简单，变长数据块可能会获得更高的数据压缩率。
2、相似文件识别。如果两个文件只有很小的差别，比如在某处插入了若干字节，找出这些数据块并单独处理，可能会提高数据压缩率。
