Enough is enough.
You can either join BAARF. Or not.
RAID-5 Write Penalty
"...If you later modify the data block it recalculates the parity by subtracting the
old block and adding in the new version then in two separate operations it
writes the data block followed by the new parity block. To do this it must
first read the parity block from whichever drive contains the parity for
that stripe block and reread the unmodified data for the updated block from
the original drive. This read-read-write-write is known as the RAID5 write
penalty since these two writes are sequential and synchronous the write
system call cannot return until the reread and both writes complete, for
safety, so writing to RAID5 is up to 50% slower than RAID0 for an array of
the same capacity. (Some software RAID5's avoid the re-read by keeping an
unmodified copy of the orginal block in memory.)"
RAID-5 Drive Failure
"Now if a drive in the RAID5 array dies, is removed, or is shut off data is
returned by reading the blocks from the remaining drives and calculating
the missing data using the parity, assuming the defunct drive is not the
parity block drive for that RAID block. Note that it takes 4 physical
reads to replace the missing disk block (for a 5 drive array) for four out
of every five disk blocks leading to a 64% performance degradation until
the problem is discovered and a new drive can be mapped in to begin
Raid-5 Failure Rate Increases
As the number of disks in a RAID 5 group increases, the Mean Time Between Failures (MTBF, the reciprocal of the failure rate) can become lower than that of a single disk.
"If you observe him closely, you will find that a geek approaches non-computer avocations in a fanatical way and always with the certainty (in keeping with an outsized opinion of himself) that he can master any subject with a dilettante's effort. In fact that seems to be the whole point of the rare excursion into non-computerized activity. Once his shallow sense of mastery is satisfied he ceases to progress in the avocation because really hard work bores him.
This is the geek as you might find him on Slashdot and in other forums arguing about Firefox or Linux or whatever his latest petty obsession is, and as I find him walking past my office day-in and day-out acting like a child. I tell you these people make feminists seem charming.
The next person to mention spaghetti stacks to me is going to have his head knocked off. -- Bill Conrad