Mirroring and RAID levels
Disk mirroring and RAID levels 0, 1, 5, 6 and 10: usable capacity, failures tolerated, parity, rebuild and hot spare, synchronous or asynchronous remote mirroring, and why a mirror does not replace a backup.
- 28 cards
- 6 topics
- Free
The outline, topic by topic
Each topic is weighted the way the exam weighs it.
- Concepts
- Questions
- Sort and link
- The numbers
- Scenarios
- Understand
A few cards from the deck
Disk mirror: what is it?
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Two or more disks that receive exactly the same writes, so that each holds a complete copy of the data.
If one disk fails, the other carries on alone. But a bad write or a deletion is applied to both copies: a mirror protects against hardware, not mistakes.
Which RAID level survives the loss of any two disks?
- RAID 6
- RAID 5
- RAID 10
- RAID 0
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RAID 6
RAID 6 keeps two parities. A RAID 10 survives two failures only if they hit two different mirrors: if they are both disks of one mirror, everything is lost.
In RAID 5, the usable capacity of n identical disks is that of … disks, because the equivalent of one disk holds the ….
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In RAID 5, the usable capacity of n identical disks is that of n − 1 disks, because the equivalent of one disk holds the parity.
The parity is spread over all the disks instead of kept on a single one. The array survives one disk failure; RAID 6 takes two parities and survives two.
Striping: what is it?
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Splitting data into stripes written in turn across several disks, to add up capacity and speed.
On its own it is RAID 0: no redundancy, and one disk failing destroys everything, so the risk grows with the number of disks.