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provisioning: explain the 'survival' number better

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This commit is contained in:
Brian Warner 2007-09-06 23:01:07 -07:00
parent 421277cafa
commit 5561d3afe4
1 changed files with 8 additions and 0 deletions
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8
src/allmydata/provisioning.py
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@ -597,6 +597,13 @@ class ProvisioningTool(rend.Page):
T.div["share data loss rate: ", T.div["share data loss rate: ",
number(share_data_loss_rate,"Bps")]) number(share_data_loss_rate,"Bps")])
# the worst-case survival numbers occur when we do a file check
# and the file is just above the threshold for repair (so we
# decide to not repair it). The question is then: what is the
# chance that the file will decay so badly before the next check
# that we can't recover it? The resulting probability is per
# check interval.
# Note that the chances of us getting into this situation are low.
P_disk_failure_during_interval = (drive_failure_rate * P_disk_failure_during_interval = (drive_failure_rate *
file_check_interval) file_check_interval)
disk_failure_dBF = 10*math.log10(P_disk_failure_during_interval) disk_failure_dBF = 10*math.log10(P_disk_failure_during_interval)
@ -614,6 +621,7 @@ class ProvisioningTool(rend.Page):
user_files_survives_dBA, user_files_survives_dBA,
"all files in grid = %d dBA" % "all files in grid = %d dBA" %
all_files_survives_dBA, all_files_survives_dBA,
" (per worst-case check interval)",
]) ])