Lecture 38

Lecture 38 - ECE52 Spring 11 Lecture 38 4/18/11 Lab...

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1 ECE52 Spring 11 Lecture 38 4/18/11 Lab practical Project due dates Exam HW 10, 11
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RAID RAID 0: No redundancy, no error tolerance, no parity, good performance: Stripe data across all available volumes – have multiple physical disks reading parts of same file at same time 2 RAID figures from Wikimedia commons
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RAID 1 Mirroring – seems wasteful, but since 1 disk is so big these days, 2 disks is the least one can often do! Great read performance (read from both, use whichever gets in first), But most inefficient RAID level. On fail, can rebuild new spare from good disk 3
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RAID 2 Hamming code! Bit-level striping plus ECC parity. Just as for memory, use, say, 4 data disks with 3 parity disks (or 32+6…) – use parity disks to identify which bit (and therefore which disk) is bad NO COMMERCIAL USE! Overkill, as we shall see – disks have internal error correction; don’t usually encounter scenario of failed bit but don’t know which one! 4
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RAID 3 Is byte-level striping plus single dedicated parity drive Low overhead, but all requests use all drives, so simultaneous accesses inhibited Parity, PLUS KNOWLEDGE OF WHICH DISK IS BAD, permits reconstruction! 5
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RAID 4 Is subtly different – block -level striping plus dedicated parity drive Again, knowledge of which drive failed plus parity permits reconstruction
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This note was uploaded on 07/05/2011 for the course ECE 52 taught by Professor Dr.jonathanboard during the Spring '11 term at Duke.

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Lecture 38 - ECE52 Spring 11 Lecture 38 4/18/11 Lab...

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