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Date:      Thu, 07 Nov 2013 16:08:14 -0500
From:      Charles Owens <cowens@greatbaysoftware.com>
To:        Mark Johnston <markj@freebsd.org>
Cc:        Jason Damron <jdamron@greatbaysoftware.com>, freebsd-scsi@freebsd.org, Steve McCoy <smccoy@greatbaysoftware.com>
Subject:   Re: adding BBU relearn support to mfiutil
Message-ID:  <527C013E.3070607@greatbaysoftware.com>
In-Reply-To: <20131107194402.GA1695@charmander.sandvine.com>
References:  <20130304033836.GA33631@oddish> <1365196956.17311.13.camel@localhost> <20130406000809.GA96223@raichu> <527A7603.7090303@greatbaysoftware.com> <20131106230356.GA86666@charmander.sandvine.com> <527BD440.8010701@greatbaysoftware.com> <20131107194402.GA1695@charmander.sandvine.com>

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On 11/7/13 2:44 PM, Mark Johnston wrote:
> On Thu, Nov 07, 2013 at 12:56:16PM -0500, Charles Owens wrote:
>> On 11/6/13 6:03 PM, Mark Johnston wrote:
>>> On Wed, Nov 06, 2013 at 12:01:55PM -0500, Charles Owens wrote:
>>>> Hi, we've been playing with this patch in the context of 8.4-RELEASE-p4
>>>> (we extracted r250483 and r250497 from stable/8 and applied to
>>>> releng/8.4).  I'm seeing some results that make me question whether or
>>>> not caching is really working correctly after a BBU relearn operation
>>>> has completed -- or maybe whether or not the new BBU patch is talking to
>>>> LSI controller properly.
>>>>
>>>> Our test system had a BBU in the failed state (relearn needed).  We used
>>>> the "start learn command" and it seemed to go well, but strangely, when
>>>> process is seems to have completed, and now several days later, status
>>>> is still LEARN_CYCLE_REQUESTED (as seen with "mfiutil show battery").
>>>> This may be entirely normal -- maybe it says that because the autolearn
>>>> feature is now enabled?
>>> I suspect that the status is bogus and that the battery is in fact dead.
>>> There seem to be a few firmware bugs in the BBU status reporting, at
>>> least with iBBU07. In your output below, I see:
>>>
>>>           Design Capacity: 1215 mAh
>>>      Full Charge Capacity: 65262 mAh
>>>          Current Capacity: 61543 mAh
>>>
>>> which clearly isn't right. I've seen this problem before as well: over
>>> time, the full charge capacity decreases, and eventually it seems to
>>> wrap around to 65535. MegaCli (LSI's binary RAID management tool) reports
>>> exactly the same thing, so it's a problem with the controller firmware.
>>> If you look at MegaCli output you get things like "Absolute charge: 6000%".
>>> So I suspect that the status is incorrect as well; when I've run into
>>> this problem, I still see "status: normal".
>>>
>>>> The "cache" status command also suggests also is a bit strange. Here is
>>>> the raw output of these status commands:
>>>>
>>>> # mfiutil cache mfid0
>>>> mfi0 volume mfid0 cache settings:
>>>>                 I/O caching: disabled
>>>>               write caching: write-back
>>>> write cache with bad BBU: disabled
>>>>                  read ahead: adaptive
>>>>           drive write cache: enabled
>>>> Cache disabled due to dead battery or ongoing battery relearn
>>>>
>>>>
>>>> # ./mfiutil show battery
>>>> mfi0: Battery State:
>>>>         Manufacture Date: 3/18/2010
>>>>            Serial Number: 77
>>>>             Manufacturer: LS1111001A
>>>>                    Model: 3598501
>>>>                Chemistry: LION
>>>>          Design Capacity: 1215 mAh
>>>>     Full Charge Capacity: 65262 mAh
>>>>         Current Capacity: 61543 mAh
>>>>            Charge Cycles: 120
>>>>           Current Charge: 94%
>>>>           Design Voltage: 3700 mV
>>>>          Current Voltage: 4081 mV
>>>>              Temperature: 23 C
>>>>         Autolearn period: 30 days
>>>>          Next learn time: Tue Nov 26 20:06:40 2013
>>>>     Learn delay interval: 0 hours
>>>>           Autolearn mode: enabled
>>>>                   Status: LEARN_CYCLE_REQUESTED
>>>>
>>>>
>>>> /Why does cache status now say  "Cache disabled due to dead battery or
>>>> ongoing battery relearn"/?  Shouldn't this no longer be the case since
>>>> I've run the "learn" operation?  Does this indicate that the I/O caching
>>>> is really disabled?
>>> I believe so. You can try changing the write caching policy to write-back
>>> with bad BBU and see if that re-enables the cache. If it does, that's
>>> more evidence that the BBU is dead and needs to be replaced.
>>>
>>>> I'd appreciate any and all assistance.  Here's a bit of other info that
>>>> might be of interest:
>>>>
>>>> # mfiutil show adapter
>>>> mfi0 Adapter:
>>>>        Product Name: Integrated Intel(R) RAID Controller SROMBSASMP2
>>>>       Serial Number:
>>>>            Firmware: 11.0.1-0036
>>>>         RAID Levels: JBOD, RAID0, RAID1, RAID5, RAID6, RAID10, RAID50
>>>>      Battery Backup: present
>>>>               NVRAM: 32K
>>>>      Onboard Memory: 512M
>>>>      Minimum Stripe: 8k
>>>>      Maximum Stripe: 1M
>>>>
>>>> # mfiutil show drives
>>>> mfi0 Physical Drives:
>>>>     1 (  136G) ONLINE    <SEAGATE ST9146852SS 0005 serial=6TB005JE> SAS E1:S0
>>>>     2 (  136G) ONLINE    <SEAGATE ST9146852SS 0005 serial=6TB005JV> SAS E1:S1
>>>>     3 (  136G) ONLINE    <SEAGATE ST9146852SS 0005 serial=6TB005KD> SAS E1:S4
>>>>     4 (  136G) ONLINE    <SEAGATE ST9146852SS 0005 serial=6TB005BQ> SAS E1:S2
>>>>     5 (  136G) HOT SPARE <SEAGATE ST9146852SS 0005 serial=6TB005FJ> SAS E1:S3
>>>>
>>>> The storage volume is 4-drives, RAID10.  System has 16GB RAM, dual Xeon
>>>> E5530 CPUs, on an Intel S5520UR motherboard.
>>> It might be useful to check the output of "mfiutil show events -c info".
>>>
>>>
>> This is good info, thank you.
>>
>> The "show events" command tells us when the battery first was detected
>> as "failed":
>>
>> 49336 (Sun Mar  3 21:53:40 UTC 2013/BATTERY/info) - Battery charge complete
>> 49340 (boot + 4s/BATTERY/info) - Battery Present
>> 49341 (boot + 4s/BATTERY/FATAL) - Battery has failed and cannot support data retention. Please replace the battery
>> 49365 (boot + 45s/BATTERY/WARN) - BBU disabled; changing WB virtual disks to WT
>> 49367 (Mon Mar  4 05:13:09 UTC 2013/BATTERY/info) - Battery temperature is normal
>>
>>
>>
>> So, given this strong indication that the BBU is really dead, and that
>> I'd still like to test the effects of write-caching, I used this
>> command:   mfiutil cache mfid0 bad-bbu-write-cache enable
>>
>> Now the "cached disabled" messages is gone:
>>
>> # mfiutil cache mfid0
>> mfi0 volume mfid0 cache settings:
>>                I/O caching: writes
>>              write caching: write-back
>> write cache with bad BBU: enabled
>>                 read ahead: adaptive
>>          drive write cache: enabled
>>
>>
>> The obvious interpretation is that write-caching is now operational (in
>> the preferred write-back mode).  Strangely, though, my performance tests
>> (with both pgbench and bonnie) still showed no meaningful effect from
>> having the cache operational!  I toggled between caching / no-caching
>> with these commands:
>>
>> # mfiutil cache mfid0 writes
>> Setting write cache policy to write-back
>>
>> # mfiutil cache mfid0 disable
>> Disabling caching of I/O writes
>>
>>
>> Again, no difference in performance was seen.
>>
>> On a whim, I also tried write-through mode, and to my surprise, bonnie
>> showed significantly reduced performance! (consistent over multiple
>> samples)  This is really confusing.  To me it suggests that there's some
>> kind of disconnect between caching-status as seen with mfiutil and
>> caching-status in reality.  Chief exhibits being that write-caching
>> appears to have still been happening even:
>>
>>    * after the "cache mfid0 disable" command was issued, and
>>    * earlier, before the "cache mfid0 bad-bbu-write-cache enable" command
>>      was issued (when "mfiutil cache mfid0" still showed "Cache disabled
>>      due to dead battery or ongoing battery relearn").
>>
>> ** If this is the case then it suggests that the system before today was
>> in a dangerous state... actively doing write-back caching with a bad BBU
>> (despite what mfiutil claimed about the cache being disabled)! **
> Yup. That's rather frightening. :(
>
>> Your thoughts?  Is there any other way to explain this?
> Nothing that comes to mind. The reason I did some work to improve LSI BBU
> reporting was because we were noticing intermittent performance problems
> that turned out to be caused by the controller flipping to write-through
> mode during BBU relearn cycles.
>
> However, I've never bothered verifying that the cache is actually in
> write-through mode when the battery is dead. I think there's a machine
> in my lab which shows similar problems, so I will try to take a look at
> it soon, do some write perf testing and see what MegaCli reports. It'll
> take me a few days at least to get to this though.
>
> I'm not sure how this might be fixed in the case that it turns out to be
> another firmware bug.
>
> -Mark

After some reflection... I think part of the story is that before now 
I've been primarily relying on pgbench (since the vast majority of our 
application's I/O workload is with the DB). For whatever reason the 
randomized I/O that pgbench generates doesn't seem to benefit much from 
the LSI controller's write-caching -- whereas the effects of caching are 
readily visible with bonnie.  The controller may have indeed properly 
switched from WB-to-WT as the BBU failed (and as reported in the 
controller events log)... but my focus on pgbench results led me to 
conclude that it hadn't.  Even with what I reported above I was still 
bouncing back and forth between pgbench and bonnie... and I think the 
largely-steady pgbench results were muddying things.

If I now toggle the "bad-bbu-write-cache" setting between enable and 
disable I'm seeing (with bonnie) the expected behavior.  With it set to 
"disable", I correctly see poor performance, showing that it has dropped 
back to WT mode.  Setting it "enable" gives good performance (WB).  This 
is repeatable.

Upshot is that I'm now suspecting that what I said before was a false 
alarm (happily).  Of course, I do have a failed BBU, which is not so good.

In a couple weeks I should have access to another box with a failed BBU, 
so I'll have a chance to repeat the testing with bonnie.


-- Charles



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