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Comment Re:Ripoff (Score 1) 487

It depends - again it's a question of the numbers. Although there is some good evidence that a PS is the most likely part to fail in a rig and as such you should know what your plan is for a failure. A large storage setup could provide similar mitigation with multiple units assuming your storage pool is large enough or a less critical storage pool could be mitigated with a cold spare.

Comment Re:Not ZFS? (Score 1) 487

http://my.safaribooksonline.com/9780596521974/ch04

4.1.1. Data Integrity in HDFS

HDFS transparently checksums all data written to it and by default verifies checksums when reading data. A separate checksum is created for every io.bytes.per.checksum bytes of data. The default is 512 bytes, and since a CRC-32 checksum is 4 bytes long, the storage overhead is less than 1%.

Datanodes are responsible for verifying the data they receive before storing the data and its checksum. This applies to data that they receive from clients and from other datanodes during replication. A client writing data sends it to a pipeline of datanodes (as explained in Chapter 3), and the last datanode in the pipeline verifies the checksum. If it detects an error, the client receives a ChecksumException, a subclass of IOException.

When clients read data from datanodes, they verify checksums as well, comparing them with the ones stored at the datanode. Each datanode keeps a persistent log of checksum verifications, so it knows the last time each of its blocks was verified. When a client successfully verifies a block, it tells the datanode, which updates its log. Keeping statistics such as these is valuable in detecting bad disks.

Aside from block verification on client reads, each datanode runs a DataBlockScanner in a background thread that periodically verifies all the blocks stored on the datanode. This is to guard against corruption due to "bit rot" in the physical storage media. See Section 10.1.4.3 for details on how to access the scanner reports.

Image

Teacher Sells Ads On Tests 532

Tom Farber, a calculus teacher at Rancho Bernardo high school in San Diego, has come up with a unique way of covering district cuts to his supplies budget. He sells ads on his tests. "Tough times call for tough actions," Tom says. The price of an ad on a Mr. Farber Calc test is as follows: $10 for a quiz, $20 for a chapter test, and $30 for a semester final. Most of the ads are messages from parents but about a third of them come from local businesses. Principal Paul Robinson says reaction has been "mixed," but adds, "It's not like, 'This test is brought to you by McDonald's or Nike.'" I see his point. Being a local business whore is much better than being a multinational conglomerate whore.
Portables (Apple)

Submission + - iPod Touch screen problems - defect or design? 2

The Blue Meanie writes: As reported by a friend of mine, and confirmed with a thread or two elsewhere, people are noticing that a number of the new iPod Touch screens are producing really BAD video, especially in darker areas. Is this just a case of Apple picking a lousy screen for this model, or is this a manufacturing defect? They obviously didn't use the screen from the iPhone — are Touch users destined to suffer with sub-par video?

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