Re: File system compression, not at the block layer

From: Timothy Miller
Date: Fri Apr 23 2004 - 16:24:23 EST

Ben Greear wrote:
Richard B. Johnson wrote:

Actually not. You need a FIFO to cache your bits into buffers of bytes
anyway. Depending upon the length of the FIFO, you can "rubber-band" a
lot of rotational latency. When you are dealing with a lot of drives,
you are never going to have all the write currents turn on at the same
time anyway because they are (very) soft-sectored, i.e., block
replacement, etc.

Wouldn't this pretty much guarantee worst-case latency scenario for reading, since
on average at least one of your 32 disks is going to require a full rotation
(and probably a seek) to find it's bit?

Only for the first bit of a block. For large streams of reads, the fifos will keep things going, except for occasionally as drives drift in their relative rotation positions which can cause some delays.

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