数据很重要、数据很重要、数据很重要！！！
重要的话说三遍，话说自己买了个黑群晖，6盘位的，就是为了保存照片和数据......
其实1盘和2盘的nas都是耍流氓，根本无用，必须是4盘位以上的才勉强可靠。所以才买的这个黑群晖，只买了3个盘做了raid5，侥是如此，真的是莫名坏了一块，好在在保修期内，更换一块后故障解除，期间倒腾2块盘的数据依然是噩梦啊。
那么数据如此重要，那么怎么做到完全的备份呢？
数据是3盘raid5，已经有保证了，剩下就是系统也必须有备份可恢复才可以
群晖本质是linux，文件系统是mdadm+lvm，所以备份也必须从这个方向开始。
首先是备份启动的usb盘，先fdisk -l 看一下：
Disk /dev/sda: 2000.3 GB, 2000398934016 bytes
255 heads, 63 sectors/track, 243201 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sda1 1 311 2490240 fd Linux raid autodetect
Partition 1 does not end on cylinder boundary
/dev/sda2 311 572 2097152 fd Linux raid autodetect
Partition 2 does not end on cylinder boundary
/dev/sda3 588 243201 1948793440+ fd Linux raid autodetect
Disk /dev/sdb: 2000.3 GB, 2000398934016 bytes
255 heads, 63 sectors/track, 243201 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sdb1 1 311 2490240 fd Linux raid autodetect
Partition 1 does not end on cylinder boundary
/dev/sdb2 311 572 2097152 fd Linux raid autodetect
Partition 2 does not end on cylinder boundary
/dev/sdb3 588 243201 1948793440+ fd Linux raid autodetect
Disk /dev/sdc: 2000.3 GB, 2000398934016 bytes
255 heads, 63 sectors/track, 243201 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sdc1 1 311 2490240 fd Linux raid autodetect
Partition 1 does not end on cylinder boundary
/dev/sdc2 311 572 2097152 fd Linux raid autodetect
Partition 2 does not end on cylinder boundary
/dev/sdc3 588 243201 1948793440+ fd Linux raid autodetect
Disk /dev/sdu: 4227 MB, 4227858432 bytes
4 heads, 32 sectors/track, 64512 cylinders
Units = cylinders of 128 * 512 = 65536 bytes
Device Boot Start End Blocks Id System
/dev/sdu1 * 1 256 16352+ e Win95 FAT16 (LBA)
3块2T的盘，每个盘有3个分区，然后最后是USB盘，盘符sdu，备份它
dd if=/dev/sdu |gzip -c > /root/usb.img
USB盘备好了，下面得备份raid了，先查看raid信息：
cat /proc/mdstat
Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
md2 : active raid5 sda3[0] sdc3[2] sdb3[1]
3897584512 blocks super 1.2 level 5, 64k chunk, algorithm 2 [3/3] [UUU]
md1 : active raid1 sda2[0] sdb2[1] sdc2[2]
2097088 blocks [12/3] [UUU___]
md0 : active raid1 sda1[0] sdb1[1] sdc1[2]
2490176 blocks [12/3] [UUU___]
看来有三个raid组，md0和md1是raid1，md2是raid5
md0的组员是sda1、sdb1、sdc1
md1的组员是sda2、sdb2、sdc2
md2的组员是sda3、sdb3、sdc3
三个盘的分区应该是一样的，我们看一个即可：
fdisk -l /dev/sda
Disk /dev/sda: 2000.3 GB, 2000398934016 bytes
255 heads, 63 sectors/track, 243201 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sda1 1 311 2490240 fd Linux raid autodetect
Partition 1 does not end on cylinder boundary
/dev/sda2 311 572 2097152 fd Linux raid autodetect
Partition 2 does not end on cylinder boundary
/dev/sda3 588 243201 1948793440+ fd Linux raid autodetect
我们可以看到是2T的盘，三个分区的起始柱头信息都很清晰，记录下来。
所以，如果坏了，看看分区，分区没坏直接进行下一步，分区坏了的话，我们先fdisk分好区，然后开始修复：
查看各个md的uuid：
mdadm --examine --scan /dev/sda1 /dev/sdb1 /dev/sdc1
ARRAY /dev/md0 UUID=35d393bd:1f4dde6b:3017a5a8:c86610be
mdadm --examine --scan /dev/sda2 /dev/sdb2 /dev/sdc2
ARRAY /dev/md1 UUID=8f02f0d4:e249900a:3017a5a8:c86610be
mdadm --examine --scan /dev/sda3 /dev/sdb3 /dev/sdc3
ARRAY /dev/md/2 metadata=1.2 UUID=d1411045:24723563:3a19cef5:07732afa name=DiskStation:2
修复的时候，根据上面信息，编辑生成/etc/mdadm.conf，注意顺序是倒的， md0->md1->md2，devices中如果一块盘坏了，改成missing......
DEVICE partitions
ARRAY /dev/md0 level=raid1 num-devices=2
↪UUID=b3cd99e7:d02be486:b0ea429a:e18ccf65
↪devices=/dev/sda1,missing
ARRAY /dev/md1 level=raid1 num-devices=2
↪UUID=75fa22aa:9a11bcad:b42ed14a:b5f8da3c
↪devices=/dev/sda2,missing
ARRAY /dev/md2 level=raid1 num-devices=2
↪UUID=532502de:90e44fb0:242f485f:f02a2565
↪devices=/dev/sda3,missing
然后刷新raid并查看raid是否正常
mdadm -A -s
cat /proc/mdstat
如果要全面毁了盘阵，重建md，方法如下：
mdadm --create --verbose /dev/md0 --level=1 --raid-devices=3 /dev/sda1 /dev/sdb1 /dev/sdc1
mdadm --create --verbose /dev/md1 --level=1 --raid-devices=3 /dev/sda2 /dev/sdb2 /dev/sdc2
mdadm --create --verbose /dev/md0 --level=5 --raid-devices=3 /dev/sda3 /dev/sdb3 /dev/sdc3
上面已经做好了RAID部分MD的备份。LVM是基于MD之上的，下面我们来备份LVM。
首先查看卷信息：
DiskStation> pvdisplay
--- Physical volume ---
PV Name /dev/md2
VG Name vg1
PV Size 3.63 TB / not usable 2.88 MB
Allocatable yes (but full)
PE Size (KByte) 4096
Total PE 951558
Free PE 0
Allocated PE 951558
PV UUID 5li2xk-tZdQ-c63W-qpM7-jo9F-5xGg-xFP1Wr
DiskStation> vgdisplay
--- Volume group ---
VG Name vg1
System ID
Format lvm2
Metadata Areas 1
Metadata Sequence No 3
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 2
Open LV 1
Max PV 0
Cur PV 1
Act PV 1
VG Size 3.63 TB
PE Size 4.00 MB
Total PE 951558
Alloc PE / Size 951558 / 3.63 TB
Free PE / Size 0 / 0
VG UUID UUCftW-HIFK-vmL0-0MTG-XzOT-BCTI-okhVf3
DiskStation> lvdisplay
--- Logical volume ---
LV Name /dev/vg1/syno_vg_reserved_area
VG Name vg1
LV UUID BmrrfE-vjMY-rJO8-C7OP-2los-KfeO-1hBrWb
LV Write Access read/write
LV Status available
# open 0
LV Size 12.00 MB
Current LE 3
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 384
Block device 253:0
--- Logical volume ---
LV Name /dev/vg1/volume_1
VG Name vg1
LV UUID 80vCET-1yH4-KMXS-E0N7-3tiP-m24I-Gzw7ij
LV Write Access read/write
LV Status available
# open 1
LV Size 3.63 TB
Current LE 951555
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 4096
Block device 253:1
ok, 备份
vgcfgbackup
备份文件会放到/etc/lvm/backup/vg1，把这个文件拷走.
如果要恢复：
vgcfgrestore -f vg1 vg1
pvscan
vgscan
lvscan
把u盘文件、fdisk文件、lvm的文件拷出来放到dropbox，一切就妥当了。