amrd disk performance drop after running under high load

Alexey Popov lol at
Tue Nov 13 04:49:04 PST 2007


Panagiotis Christias wrote:
>>>>> In the "good" case you are getting a much higher interrupt rate but
>>>>> with the data you provided I can't tell where from.  You need to run
>>>>> vmstat -i at regular intervals (e.g. every 10 seconds for a minute)
>>>>> during the "good" and "bad" times, since it only provides counters
>>>>> and an average rate over the uptime of the system.
>>>> Now I'm running 10-process lighttpd and the problem became no so big.
>>>> I collected interrupt stats and it shows no relation beetween
>>>> ionterrupts and slowdowns. Here is it:
>>>> Also I have similiar statistics on mutex profiling and it shows
>>>> there's no problem in mutexes.
>>>> I have no idea what else to check.
>>> I don't know what this graph is showing me :)  When precisely is the
>>> system behaving poorly?
> what is your RAID controller configuration (read ahead/cache/write
> policy)? I have seen weird/bogus numbers (~100% busy) reported by
> systat -v when read ahead was enabled on LSI/amr controllers.

               Existing Logical Drive Information
               By LSI Logic Corp.,USA

           [Note: For SATA-2, 4 and 6 channel controllers, please specify
           Ch=0 Id=0..15 for specifying physical drive(Ch=channel,

           Logical Drive : 0( Adapter: 0 ):  Status: OPTIMAL
         SpanDepth :01     RaidLevel: 5  RdAhead : Adaptive  Cache: DirectIo
         StripSz   :064KB   Stripes  : 6  WrPolicy: WriteBack

         Logical Drive 0 : SpanLevel_0 Disks
         Chnl  Target  StartBlock   Blocks      Physical Target Status
         ----  ------  ----------   ------      ----------------------
         0      00    0x00000000   0x22ec0000   ONLINE
         0      01    0x00000000   0x22ec0000   ONLINE
         0      02    0x00000000   0x22ec0000   ONLINE
         0      03    0x00000000   0x22ec0000   ONLINE
         0      04    0x00000000   0x22ec0000   ONLINE
         0      05    0x00000000   0x22ec0000   ONLINE

I tried to run with disabled Read-ahead, but it didn't help.

With best regards,
Alexey Popov
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