Linux
為什麼 Raid 5 陣列的空間不等於磁碟的總和？
我正在嘗試從四個磁碟創建 raid 5：
Disk /dev/sdc: 8001.6 GB, 8001563222016 bytes /dev/sdc1 2048 4294967294 2147482623+ fd Linux raid autodetect Disk /dev/sdb: 8001.6 GB, 8001563222016 bytes /dev/sdb1 2048 4294967294 2147482623+ fd Linux raid autodetect Disk /dev/sdd: 24003.1 GB, 24003062267904 bytes /dev/sdd1 2048 4294967294 2147482623+ fd Linux raid autodetect Disk /dev/sde: 8001.6 GB, 8001563222016 bytes /dev/sde1 2048 4294967294 2147482623+ fd Linux raid autodetect但是，創建後我剛剛獲得了 6T 空間（我的磁碟之一）：
/dev/md0 ext4 6.0T 184M 5.7T 1% /mnt/raid5這是我創建過程的其他資訊：
結果
mdadm -E /dev/sd[b-e]1：/dev/sdb1: Magic : a92b4efc Version : 1.2 Feature Map : 0x0 Array UUID : 8953b4f1:61212c46:b0a63144:25eb4a7d Name : node7:0 (local to host node7) Creation Time : Fri Sep 7 09:16:42 2018 Raid Level : raid5 Raid Devices : 4 Avail Dev Size : 4294703103 (2047.87 GiB 2198.89 GB) Array Size : 6442053120 (6143.62 GiB 6596.66 GB) Used Dev Size : 4294702080 (2047.87 GiB 2198.89 GB) Data Offset : 262144 sectors Super Offset : 8 sectors State : clean Device UUID : 2fcb3346:9ed69eab:64c6f851:0bcc39c4 Update Time : Fri Sep 7 13:17:38 2018 Checksum : c701ff7e - correct Events : 18 Layout : left-symmetric Chunk Size : 512K Device Role : Active device 0 Array State : AAAA ('A' == active, '.' == missing) /dev/sdc1: Magic : a92b4efc Version : 1.2 Feature Map : 0x0 Array UUID : 8953b4f1:61212c46:b0a63144:25eb4a7d Name : node7:0 (local to host node7) Creation Time : Fri Sep 7 09:16:42 2018 Raid Level : raid5 Raid Devices : 4 Avail Dev Size : 4294703103 (2047.87 GiB 2198.89 GB) Array Size : 6442053120 (6143.62 GiB 6596.66 GB) Used Dev Size : 4294702080 (2047.87 GiB 2198.89 GB) Data Offset : 262144 sectors Super Offset : 8 sectors State : clean Device UUID : 6f13c9f0:de2d4c6f:cbac6b87:67bc483e Update Time : Fri Sep 7 13:17:38 2018 Checksum : e4c675c2 - correct Events : 18 Layout : left-symmetric Chunk Size : 512K Device Role : Active device 1 Array State : AAAA ('A' == active, '.' == missing) /dev/sdd1: Magic : a92b4efc Version : 1.2 Feature Map : 0x0 Array UUID : 8953b4f1:61212c46:b0a63144:25eb4a7d Name : node7:0 (local to host node7) Creation Time : Fri Sep 7 09:16:42 2018 Raid Level : raid5 Raid Devices : 4 Avail Dev Size : 4294703103 (2047.87 GiB 2198.89 GB) Array Size : 6442053120 (6143.62 GiB 6596.66 GB) Used Dev Size : 4294702080 (2047.87 GiB 2198.89 GB) Data Offset : 262144 sectors Super Offset : 8 sectors State : clean Device UUID : 4dab38e6:94c5052b:06d6b6b0:34a41472 Update Time : Fri Sep 7 13:17:38 2018 Checksum : f306b65f - correct Events : 18 Layout : left-symmetric Chunk Size : 512K Device Role : Active device 2 Array State : AAAA ('A' == active, '.' == missing) /dev/sde1: Magic : a92b4efc Version : 1.2 Feature Map : 0x0 Array UUID : 8953b4f1:61212c46:b0a63144:25eb4a7d Name : node7:0 (local to host node7) Creation Time : Fri Sep 7 09:16:42 2018 Raid Level : raid5 Raid Devices : 4 Avail Dev Size : 4294703103 (2047.87 GiB 2198.89 GB) Array Size : 6442053120 (6143.62 GiB 6596.66 GB) Used Dev Size : 4294702080 (2047.87 GiB 2198.89 GB) Data Offset : 262144 sectors Super Offset : 8 sectors State : clean Device UUID : b04d152e:0448fe56:3b22a2d6:b2504d26 Update Time : Fri Sep 7 13:17:38 2018 Checksum : 40ffd3e7 - correct Events : 18 Layout : left-symmetric Chunk Size : 512K Device Role : Active device 3 Array State : AAAA ('A' == active, '.' == missing)結果
mdadm --detail /dev/md0：/dev/md0: Version : 1.2 Creation Time : Fri Sep 7 09:16:42 2018 Raid Level : raid5 Array Size : 6442053120 (6143.62 GiB 6596.66 GB) Used Dev Size : 2147351040 (2047.87 GiB 2198.89 GB) Raid Devices : 4 Total Devices : 4 Persistence : Superblock is persistent Update Time : Fri Sep 7 13:17:38 2018 State : clean Active Devices : 4 Working Devices : 4 Failed Devices : 0 Spare Devices : 0 Layout : left-symmetric Chunk Size : 512K Name : node7:0 (local to host node7) UUID : 8953b4f1:61212c46:b0a63144:25eb4a7d Events : 18 Number Major Minor RaidDevice State 0 8 17 0 active sync /dev/sdb1 1 8 33 1 active sync /dev/sdc1 2 8 49 2 active sync /dev/sdd1 4 8 65 3 active sync /dev/sde1結果
mkfs.ext4 /dev/md0mke2fs 1.41.9 (22-Aug-2009) Filesystem label= OS type: Linux Block size=4096 (log=2) Fragment size=4096 (log=2) 402628608 inodes, 1610513280 blocks 80525664 blocks (5.00%) reserved for the super user First data block=0 Maximum filesystem blocks=4294967296 49149 block groups 32768 blocks per group, 32768 fragments per group 8192 inodes per group Superblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 4096000, 7962624, 11239424, 20480000, 23887872, 71663616, 78675968, 102400000, 214990848, 512000000, 550731776, 644972544 Writing inode tables: done Creating journal (32768 blocks): done Writing superblocks and filesystem accounting information: done This filesystem will be automatically checked every 37 mounts or 180 days, whichever comes first. Use tune2fs -c or -i to override.然後
mkdir /mnt/raid5和mount /dev/md0 /mnt/raid5/。
6 TB 將是 (4 - 1) * 2 TB，其中 4 是您的設備數量，減去 1 表示奇偶校驗，2 TB 是您似乎擁有的分區大小。
假設第一個輸出來自
fdisk實用程序，這些欄位可能是partition name start end length type /dev/sdc1 2048 4294967294 2147482623+ fd Linux raid autodetect以 512 字節扇區為單位，分區從頭到尾為 2 TB。（
+長度欄位末尾的似乎暗示實際長度大於 ，所以我忽略了該欄位。）我的fdisk實用程序也以人類單位顯示分區的大小，但 2 TB 是舊的限制-style MBR 分區表可以提供，因此請檢查您是否沒有使用它而不是 GPT。一些舊版本的
fdisk可能不知道 GPT 分區表，因此您可能需要使用其他工具（或獲取更新版本）。你實際上甚至不需要使用分區，你可以mdadm在/dev/sd[bcde]. 但請注意，由於 RAID-5 佈局，最小的驅動器（或分區）設置了陣列的大小，因此單個較大的磁碟會部分浪費。