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Old 07-22-2014, 12:40 PM   #1
nixboy
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Question using space on 2 raid disks


hi,

i am given with 2x500gb software raid-1 disks.

my question is..
1. how much space i get in total from both disks?
2. how i can use space on 2nd disk?

sorry.. i'm new to linux..
 
Old 07-22-2014, 12:45 PM   #2
TobiSGD
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1. 500GB. RAID-1 is mirroring, everything that is written to disk 1 is also written to disk 2.
2. You can't. All disks (or better partitions) in a RAID are handled as one entity, you don't have (and don't need) to access the separate disks.
 
Old 07-22-2014, 01:58 PM   #3
suicidaleggroll
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To further answer the question:

RAID 0 - Striping - any data written to the array is split between all disks (for a 2-drive RAID, half is written to each). Array size is the sum of the independent disks, read and write speeds are both increased over a single drive, and there is no redundancy (lose one drive and you lose everything). Typically used when speed is essential and the user has no regard for data integrity.

RAID 1 - Mirroring - any data written to the array is duplicated on all disks. Array size is the size of one disk, write speed is the same vs a single drive, read speed can be higher depending on the controller, and there is N-1 drives of redundancy (you don't lose any data until you've lost every single drive in the array). Typically used when data integrity is essential and the user doesn't care so much about speed/storage space.

RAID 10 - Striping + Mirroring - a combination of 1 and 0 above (hence the "10"), requires 4 disks. Array size is the sum of two of the disks, read and write speeds are both increased over a single drive, and you have at least one drive of redundancy, possibly two (depends on which drives fail). Typically used in 4-drive systems as a mix of 0 and 1, when speed and integrity are both important, but the user doesn't want to use the additional CPU overhead required for the parity calculations in RAID 5 or 6.

RAID 5 - Parity - like 0, but with an extra parity drive. Array size is the sum of N-1 independent disks, read and write speeds are both increased over a single drive, but CPU overhead is increased, and you have 1 drive of redundancy (lose one drive and you're ok, lose 2 and you lose everything). Typically used in 3-8 drive arrays when speed and limited integrity are both important. Care must be taken when used with large arrays or large disks, as the excessive time required to rebuild after a failure opens up a window when the system is vulnerable.

RAID 6 - Double Parity - like 5, but with two parity drives. Array size is the sum of N-2 independent disks, read and write speeds are both increased, but CPU overhead is significantly increased, and you have 2 drives of redundancy (lose 1-2 drives and you're ok, lose 3 and you lose everything). Typically used in large arrays when speed and integrity are both important. Pretty much requires a hardware RAID controller in order to handle the double parity calculations with minimal impact.

Then you have 50 and 60 for even larger arrays - like 10 they're just a combination of 5/6 and 0.

Last edited by suicidaleggroll; 07-22-2014 at 02:02 PM.
 
Old 07-22-2014, 03:06 PM   #4
nixboy
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@TobiSGD @suicidaleggroll

Thanks a lot bros.. now I understood it.
 
  


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