Hello,
Recently we find a bug about skip_copy feature in raid5 degraded mode.
In the beginning, we enable the skip_copy feature to speed up system’s
write performance. But when the system has database read/write I/O
continually in raid5 degraded mode, the Mongo DB will detect the
checksum error and generate related debug log. The following is the
testing detail.
a. Enable skip_copy
--> Checksum error logs from Mongo DB
2017-02-06T11:54:56.537+0800 E STORAGE [conn7] WiredTiger (0)
[1486353296:537114][52:0x7f98396a4700],
file:collection-110-3235234017846331078.wt, WT_CURSOR.next: read
checksum error for 4096B block at offset 61440: calculated block
checksum of 1363526237 doesn't match expected checksum of 2969711960
b. Disable skip_copy
--> Mongo DB has no checksum error.
We've pretty sure that it must be a bug by our repeated database I/O
testing. When skip_copy feature is enabled, the raid5/raid6 always
causes the mongo DB checksum error in degraded mode less than one
hour. On the contrary, it will never cause this abnormal situation
when the skip_copy feature is disabled. Besides, because the skip_copy
feature only affects the write action instead of read action, I think
it should be the write action in degraded mode while skip_copy feature
is enabled cause this bug.
Please kindly provide us some help or idea about the root cause and solution.
Thanks,
--
Chien Lee
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