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两个阵列的阵列大小略有不同，且磁盘/分区大小相同，为什么？

tag-icon • tag-icon raid mdadm software-raid
两个阵列的阵列大小略有不同，且磁盘/分区大小相同，为什么？

一年前，我使用 CentOS 6.3 附带的 mdadm v3.2.x 创建了一个软件 RAID 5 阵列，几个月后，我将阵列移动/组装到 Fedora 19（现在的 Fedora 20）中。

它有三个 3TB 磁盘（希捷ST3000DM001），它几乎已满，所以我添加了 2 个磁盘，并将阵列增长到 4 个磁盘 + 1 个热备用磁盘。现在它的大小是8383.55 GiB。

# mdadm -D /dev/md127 
/dev/md127:
        Version : 1.2
  Creation Time : Fri Jan 11 17:56:18 2013
     Raid Level : raid5
     Array Size : 8790792192 (8383.55 GiB 9001.77 GB)
  Used Dev Size : 2930264064 (2794.52 GiB 3000.59 GB)
   Raid Devices : 4
  Total Devices : 5
    Persistence : Superblock is persistent

    Update Time : Tue Mar 25 11:04:15 2014
          State : clean 
 Active Devices : 4
Working Devices : 5
 Failed Devices : 0
  Spare Devices : 1

         Layout : left-symmetric
     Chunk Size : 512K

           Name : RecordBackup01:127  (local to host RecordBackup01)
           UUID : dfd3bbe7:4b0231fe:9007bc4a:e106acac
         Events : 7264

    Number   Major   Minor   RaidDevice State
       0       8       17        0      active sync   /dev/sdb1
       1       8       33        1      active sync   /dev/sdc1
       3       8       49        2      active sync   /dev/sdd1
       5       8       81        3      active sync   /dev/sdf1

       4       8       65        -      spare   /dev/sde1

然后，我使用 mdadm v3.3（从 Fedora 20 附带）和 5 个 3TB 磁盘（东芝）创建了另一个阵列 (RAID 6)DT01ACA300），但它的大小是8383.18吉布，略小于 8383.55 GiB。

# mdadm -D /dev/md127 
/dev/md127:
        Version : 1.2
  Creation Time : Fri Mar 21 18:12:00 2014
     Raid Level : raid6
     Array Size : 8790402048 (8383.18 GiB 9001.37 GB)
  Used Dev Size : 2930134016 (2794.39 GiB 3000.46 GB)
   Raid Devices : 5
  Total Devices : 5
    Persistence : Superblock is persistent

  Intent Bitmap : Internal

    Update Time : Tue Mar 25 11:18:51 2014
          State : active 
 Active Devices : 5
Working Devices : 5
 Failed Devices : 0
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 512K

           Name : RecordBackup02:127  (local to host RecordBackup02)
           UUID : 923c9658:12739258:506fc8b0:f8c5edf3
         Events : 8172

    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
       3       8       65        3      active sync   /dev/sde1
       4       8       81        4      active sync   /dev/sdf1

两个阵列中每个磁盘的分区大小是相同的（所有分区都有5860531087个逻辑扇区，见下面的分区信息），那么为什么阵列大小不同呢？是由不同的 mdadm 版本或不同的数组级别还是其他原因引起的？

阵列 1 (RAID 5) 磁盘/分区信息

# LANG=en parted /dev/sdb "unit s print all"                                                                                        
Model: ATA ST3000DM001-1CH1 (scsi)
Disk /dev/sdb: 5860533168s
Sector size (logical/physical): 512B/4096B
Partition Table: gpt
Disk Flags: 

Number  Start  End          Size         File system  Name  Flags
 1      2048s  5860533134s  5860531087s               pri


Model: ATA ST3000DM001-1CH1 (scsi)
Disk /dev/sdc: 5860533168s
Sector size (logical/physical): 512B/4096B
Partition Table: gpt
Disk Flags: 

Number  Start  End          Size         File system  Name     Flags
 1      2048s  5860533134s  5860531087s  ext4         primary


Model: ATA ST3000DM001-1CH1 (scsi)
Disk /dev/sdd: 5860533168s
Sector size (logical/physical): 512B/4096B
Partition Table: gpt
Disk Flags: 

Number  Start  End          Size         File system  Name     Flags
 1      2048s  5860533134s  5860531087s  ext4         primary


Model: ATA ST3000DM001-1CH1 (scsi)
Disk /dev/sde: 5860533168s
Sector size (logical/physical): 512B/4096B
Partition Table: gpt
Disk Flags: 

Number  Start  End          Size         File system  Name     Flags
 1      2048s  5860533134s  5860531087s               primary


Model: ATA ST3000DM001-1CH1 (scsi)
Disk /dev/sdf: 5860533168s
Sector size (logical/physical): 512B/4096B
Partition Table: gpt
Disk Flags: 

Number  Start  End          Size         File system  Name     Flags
 1      2048s  5860533134s  5860531087s               primary




Model: Linux Software RAID Array (md)
Disk /dev/md127: 17581584384s
Sector size (logical/physical): 512B/4096B
Partition Table: loop
Disk Flags: 

Number  Start  End           Size          File system  Flags
 1      0s     17581584383s  17581584384s  xfs

阵列 2 (RAID 6) 磁盘/分区信息

# LANG=en parted /dev/sdb "unit s print all"
Model: ATA TOSHIBA DT01ACA3 (scsi)
Disk /dev/sdb: 5860533168s
Sector size (logical/physical): 512B/4096B
Partition Table: gpt
Disk Flags: 

Number  Start  End          Size         File system  Name     Flags
 1      2048s  5860533134s  5860531087s               primary


Model: ATA TOSHIBA DT01ACA3 (scsi)
Disk /dev/sdc: 5860533168s
Sector size (logical/physical): 512B/4096B
Partition Table: gpt
Disk Flags: 

Number  Start  End          Size         File system  Name     Flags
 1      2048s  5860533134s  5860531087s               primary


Model: ATA TOSHIBA DT01ACA3 (scsi)
Disk /dev/sdd: 5860533168s
Sector size (logical/physical): 512B/4096B
Partition Table: gpt
Disk Flags: 

Number  Start  End          Size         File system  Name     Flags
 1      2048s  5860533134s  5860531087s               primary


Model: ATA TOSHIBA DT01ACA3 (scsi)
Disk /dev/sde: 5860533168s
Sector size (logical/physical): 512B/4096B
Partition Table: gpt
Disk Flags: 

Number  Start  End          Size         File system  Name     Flags
 1      2048s  5860533134s  5860531087s               primary


Model: ATA TOSHIBA DT01ACA3 (scsi)
Disk /dev/sdf: 5860533168s
Sector size (logical/physical): 512B/4096B
Partition Table: gpt
Disk Flags: 

Number  Start  End          Size         File system  Name     Flags
 1      2048s  5860533134s  5860531087s               primary






Model: Linux Software RAID Array (md)
Disk /dev/md127: 17580804096s
Sector size (logical/physical): 512B/4096B
Partition Table: loop
Disk Flags: 

Number  Start  End           Size          File system  Flags
 1      0s     17580804095s  17580804096s  xfs

答案1

明显的区别是：

Intent Bitmap : Internal

对于是否启用意图位图，mdadm 版本是否有不同的默认值？

据我了解，内部意图位图使用磁盘的一部分来存储它将要写入的内容，因此当您更换故障磁盘时重建时不需要验证每个块。

mdadm --bitmap=none ...尝试使用或显式创建 RAIDmdadm --bitmap=internal ...

https://raid.wiki.kernel.org/index.php/Write-intent_bitmap

答案2

你问的是尺寸……所以是的尺寸开销。我最好的猜测是，额外的奇偶校验需要某种额外的索引或其他东西（不了解 RAID6 的内部情况）。我们谈论的是 8.3 TB 的 370+ MB ...这不到总空间的 0.005%！

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