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No backup, no security.
Especially those old hard drives that don't know how many years they've been using, have some bad ways, they can't be repaired, and the data in them can't be copied. It's a real ghost.

disk array

MAC OS 10.11 and later systems, disk arrays in disk tools have disappeared, I wipe.
Explain the disk array, the simplest two, RAID0 and RAID1.
RAID0 is broken, read speed and write speed are multiples of disk number, capacity is also the sum of disk capacity, three or four pieces of RAID0, faster than SSD (solid-state hard disk)==. If it's broken, you can only cry.
RAID1 spare tire is not the same, a broken piece is replaced by another one. The capacity is calculated by the smallest. The capacity of 1T and 2T is only 1T below. The reading speed is quite acceptable, and the writing speed is negligible (so is the original slowest disk speed).

Disk Defragmentation (Command Line)

There are software, such as software RAID (like downloading cracked versions to update to the latest, otherwise it can not be used, it is a pit), but the use of disk arrays or honestly tap commands.

Let's start with a few diskutil list s

Mac-Pro-970:~ xcyxiner$ diskutil list
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *256.1 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                  Apple_HFS mac 10.11 HD            255.2 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
/dev/disk1 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.1 GB   disk1
   1:                        EFI EFI                     209.7 MB   disk1s1
   2:                 Apple_RAID                         499.8 GB   disk1s2
   3:                 Apple_Boot Boot OS X               134.2 MB   disk1s3
/dev/disk2 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.1 GB   disk2
   1:                        EFI EFI                     209.7 MB   disk2s1
   2:                 Apple_RAID                         499.8 GB   disk2s2
   3:                 Apple_Boot Boot OS X               134.2 MB   disk2s3
/dev/disk3 (internal, virtual):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS RAID1                  +499.8 GB   disk3
Mac-Pro-970:~ xcyxiner$

Then the disk array command is related to diskutil appleraid (- help is invalid, no need to lose, return directly)

Mac-Pro-970:~ xcyxiner$ diskutil appleraid
Usage:  diskutil [quiet] appleRAID|AR <raidverb> <options>,
        where <raidverb> is as follows:

     list            (Display the current status of RAID sets)
     create          (Create a RAID set on multiple disks)
     delete          (Delete an existing RAID set)
     repairMirror    (Repair a damaged RAID mirror set)
     add             (Add a spare or member disk to an existing RAID)
     remove          (Remove a spare or member disk from an existing RAID)
     enable          (Convert a volume into a single disk RAID set)
     update          (Update the settings of an existing RAID)

diskutil appleRAID <raidverb> with no options will provide help on that verb

About creating disk array diskutil apple raid, people have a complete example, do not add to the picture, mirror is raid1, stripe is raid0, level Four has not passed, the rest of their own question Du Niang. (Create backup before, it seems that the create will get rid of all the data in the hard disk....)

Mac-Pro-970:~ xcyxiner$ diskutil appleraid create
Usage:  diskutil appleRAID create mirror|stripe|concat setName
        filesystemType MemberDeviceNames|NestedRAIDSetUUIDs ...
Create a RAID set.  All existing data on the drives will be lost.
Ownership of the affected disks is required.
Example: diskutil AppleRAID create mirror MirrorName JHFS+ disk1 disk2
Mac-Pro-970:~ xcyxiner$

After the above processing, it's probably like this.

Mac-Pro-970:~ xcyxiner$ diskutil appleraid list
AppleRAID sets (1 found)
===============================================================================
Name:                 RAID1
Unique ID:            D0B4F106-6E3B-4168-9A7D-72F0EF24A9F8
Type:                 Mirror
Status:               Degraded
Size:                 499.8 GB (499763871744 Bytes)
Rebuild:              automatic
Device Node:          disk3
-------------------------------------------------------------------------------
#  DevNode   UUID                                  Status     Size
-------------------------------------------------------------------------------
0  disk2s2   6B6DFF64-A349-4683-AA71-FCC15CD5C4A7  Online     499763871744
1  disk1s2   9F927D2E-2E7A-44D9-8812-29AC0622E429  Online     499763871744
===============================================================================

Remove the hard disk from the disk array, diskutil appleraid remove, or look at the example, not to say==, generally speaking, it is the first command (remove DevNode) and the second command is to remove spare. If member is a boyfriend, spare seems to be a spare tire.

Mac-Pro-970:~ xcyxiner$ diskutil appleraid remove
Usage:  diskutil appleRAID remove MemberDeviceName|MemberUUID
        RAIDSetVolumePath|RAIDSetDeviceName|RAIDSetUUID
Remove a member or spare from an existing RAID set.
Ownership of the affected disks is required.
Example: diskutil AppleRAID remove disk2s4 /Volumes/RAID
         diskutil AppleRAID remove 11111111-2222-3333-4444-555555555555 disk5

Add a new hard disk to the disk array, diskutil Apple raid add, generally using the second (add members, spare does not know why, anyway, no, the last 11111111-2222-3333-4444-55555555 is the overall Unique ID of the raid above, such as D0B4F106-6E3B-4168-9A7D-72F0EF24A9F8)

Mac-Pro-970:~ xcyxiner$ diskutil appleraid add
Usage:  diskutil appleRAID add member|spare
        NewMemberDeviceName|NestedRAIDSetUUID
        RAIDSetVolumePath|RAIDSetDeviceName|RAIDSetUUID
Add a new member or spare to an existing RAID set.
Ownership of the affected disks is required.
Example: diskutil AppleRAID add spare disk4 /Volumes/RAID
         diskutil AppleRAID add member disk5 11111111-2222-3333-4444-555555555555

End

The best way to save money is to have a backup of the hard disk. Otherwise, you'll have to cry. ssd seems to be broken and you don't know if it can be repaired. Let's build a RAID1. It's always safe to have spare tires.