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#1
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the function of parity disk in RAID system
parity disk is used in RAID 3 & 4, how it is used in RAID system?
for example: Reading: no r/w operations on parity disk. Writing: whenever writing a block to disk, the corresponding block on parity disk should be updated. Fault Recoving: using blocks on parity disk to calculate the lost data. above is my own understanding, I don't know if it's correct, can you give me some instruction? thank you. |
#2
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Laser wrote:
parity disk is used in RAID 3 & 4, how it is used in RAID system? for example: Reading: no r/w operations on parity disk. Correct. Writing: whenever writing a block to disk, the corresponding block on parity disk should be updated. Correct. Fault Recoving: using blocks on parity disk to calculate the lost data. Correct. The recovery algorithm takes the surving blocks plus the parity block and XORs them together to recreate the missing information. -- Nik Simpson |
#3
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But how does it update the parity information when writing into one
block on data disk? I guess there are 2 approaches exists: 1. read out corresponding blocks on all other data disks, exclusive-or with the new data block, then write to correponding block on parity disk. 2. read out the old data before writing, and read out corresponding block on parity disk, then exclusive-or old data with new data and parity block, and write back to parity disk. which of above approches was implemented into actual use. why choose it? |
#4
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