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How to disable the filesystem cache on HP-UX 11i V1

How to disable the filesystem cache on HP-UX 11i V1

Hi,

We have got an reply from SAP to disable the filesystem cache on /sapdb/SID/sapdata1, /sapdb/SID/sapdata2 ....  /sapdb/SID/sapdata10 file system. As system is doing quite a lot of memory swapping (paging).

 

Please let me know if swap utilization on system is high will have performance issues?

 

Thanks,

Narendra

10 REPLIES
pradeep m
Respected Contributor

Re: How to disable the filesystem cache on HP-UX 11i V1

High swap utilsation is a factor impacting the performance. However detailed analysis is need to find actual exact cause of performance degradation.. 

 

Pls send the swapinfo output

#swapinfo -tam

 

Regards,
Pradeep

I am an HP Employee
A quick resolution to technical issues for your HP Enterprise products is just a click away HP Support Center Knowledge-base
See Self Help Post for more details


Re: How to disable the filesystem cache on HP-UX 11i V1

Hi Pradeep,

Please find the swapinfo output as below,

 

server07:[/]# swapinfo -tam
             Mb      Mb      Mb   PCT  START/      Mb
TYPE      AVAIL    USED    FREE  USED   LIMIT RESERVE  PRI  NAME
dev        4096     912    3184   22%       0       -    1  /dev/vg00/lvol2
dev        4000     909    3091   23%       0       -    1  /dev/vg00/lvswap1
dev        8192     911    7281   11%       0       -    1  /dev/vgmaxfs/lvswap2
dev        8192     915    7277   11%       0       -    1  /dev/vgmaxfs/lvswap3
dev        4080     914    3166   22%       0       -    1  /dev/vgmaxfs/lvswap4
dev        8192     914    7278   11%       0       -    1  /dev/vgmaxfs/lvswap5
dev        8192     920    7272   11%       0       -    1  /dev/vgmaxfs/lvswap6
dev        8192     916    7276   11%       0       -    1  /dev/vgmaxfs/lvswap7
dev        8192     915    7277   11%       0       -    1  /dev/vgmaxfs/lvswap8
reserve       -   29270  -29270
memory    25498    2878   22620   11%
total     86826   40374   46452   46%       -       0    -

 

Thanks,

Narendra

pradeep m
Respected Contributor

Re: How to disable the filesystem cache on HP-UX 11i V1

from the output, the swap usage is only 22% average.. If you still face any performance issue detailed analysis is need. I would recommend you to contact HP support for in depth analysis. 

 

 

Regards,
Pradeep

I am an HP Employee
A quick resolution to technical issues for your HP Enterprise products is just a click away HP Support Center Knowledge-base
See Self Help Post for more details


Dennis Handly
Acclaimed Contributor

Re: How to disable the buffer cache on HP-UX 11.11?

>We have got an reply from SAP to disable the filesystem cache on /sapdb/SID/sapdata1 ...

 

You can only disable/reduce the buffer cache on the whole system.

What are the values of dbc_max_pct(5) & dbc_min_pct(5)?

 

>if swap utilization on system is high will have performance issues?

 

Doing paging is never a good thing.  What does "vmstat 5 5" show?  (And look at the "po" column.)

Dave Olker
HPE Pro

Re: How to disable the filesystem cache on HP-UX 11i V1

> We have got an reply from SAP to disable the

> filesystem cache on /sapdb/SID/sapdata1,

> /sapdb/SID/sapdata2 .... /sapdb/SID/sapdata10

> file system. As system is doing quite a lot of memory

> swapping (paging).

 

Are you certain SAP wants all filesystem cache disabled on this system or just for these SAP filesystems?  My guess is they're really suggesting you disable caching for the SAP filesystems, not the entire system.  That would mean mounting these filesystems using either Direct I/O or Concurrent I/O.  Both of those VxFS mount options would effectively bypass the filesystem cache just for those filesystems. 

 

Can you confirm with SAP if they're recommending disabling all caching or are they suggesting you use Direct/Concurrent I/O for these SAP filesystems?

 

Dave

Re: How to disable the buffer cache on HP-UX 11.11?

Hi Dennis,

Please find the values of dbc_max_pct & dbc_min_pct as below,

dbc_max_pct                     8            
dbc_min_pct                      5

 

And also the output "vmstat 5 5" as below,

test07:[/]# vmstat 5 5
         procs           memory                            page                                  faults       cpu
    r     b     w      avm    free            re   at    pi   po    fr   de    sr     in     sy    cs  us sy id
   16     1     0  8081789  176008   19    5     6    7     0    0   104   3622  36474 28244  30 18 52
   16     1     0  8081789  175938    2    0     0    0     0    0     0   7554  97586 87950  38 53  9
   20     1     0  8354691  175938    6    0     0    0     0    0     0   6519 110868 102216  21 69 10
   20     1     0  8354691  175937    0    0     0    0     0    0     0   7116 107778 99496  33 57 10
   16     5     0  7979738  175937    7    0     0    0     0    0     0   5571 118269 110818  23 73  4

 

Thanks,

Narendra

Re: How to disable the filesystem cache on HP-UX 11i V1

Hi Dave,
SAP wants only SAP filesystems to bypass the filesystem cache. Please let me know how to bypass only the SAP filesystem cache for VxFS mounted filesystem. OS HP-UX 11i V1 (Base VERITAS Volume Manager Bundle 3.5 for HP-UX) with HP OnLineJFS 3.5 i.e. /sapdb/SID/sapdata1, /sapdb/SID/sapdata2 ....  /sapdb/SID/sapdata10.

 

Please let me know what are advantage and dis-advantage of disabling the filesystem cache.

 

Thanks,

Narendra

Re: How to disable the filesystem cache on HP-UX 11i V1

Hi Dave,

I checked an filesystem cache is disabled on the VxFS SAP filesystems as below;

server07:[/]# vxtunefs /dev/vgmaxdb/lvmaxdata1
Filesystem i/o parameters for /sapdb/SID/sapdata1
read_pref_io = 65536
read_nstream = 1
read_unit_io = 65536
write_pref_io = 65536
write_nstream = 1
write_unit_io = 65536
pref_strength = 10
buf_breakup_size = 131072
discovered_direct_iosz = 262144
max_direct_iosz = 1048576
default_indir_size = 8192
qio_cache_enable = 0
write_throttle = 0
max_diskq = 1048576
initial_extent_size = 1
max_seqio_extent_size = 2048
max_buf_data_size = 8192
hsm_write_prealloc = 0
read_ahead = 1

 

Please can you let me know how to enable the direct I/O on hp-ux VxFS filesystem? And also how to check if VxFS filesystem is already enabled for direct I/O?

Is this how we can enable the direct I/O for filesystem

    • Use the following mount options in /etc/fstab: convosync=direct,mincache=direct,delaylog,nodatainlog

                    e.g.

                    /dev/vg01/lvol1  /test   vxfs convosync=direct,mincache=direct,delaylog,nodatainlog 0 2

 

And also can I install the latest VxFS software i.e. VxFS 5.0.1 on HP-UX 11i V1 on PA-RISC server RP7400. Or any other VxFS version which supports Concurrent I/O (CIO). And also we have default VxFS (Base VERITAS Volume Manager Bundle 3.5 for HP-UX) with HP OnLineJFS 3.5). Do we have to purchase VERITAS VxFS other version than default which is available on HP-UX 11i V1 OS.

 

And also it looks like i can - For systems with >=40GB Memory set the buffercache/filecache to 1% of Physical Memory (since the cache is not used by direct I/O).  e.g. dbc_max_pct=dbc_min_pct=1 (HP-UX 11.11/11.23) .

 

Thanks,

Narendra

Dennis Handly
Acclaimed Contributor

Re: How to disable the buffer cache on HP-UX 11.11?

>Please find the values of dbc_max_pct & dbc_min_pct as below,

>dbc_max_pct                     8       dbc_min_pct                      5

 

Your buffer cache seems small enough.

 

>And also the output "vmstat 5 5" as below,

         procs           memory                            page
    r     b     w      avm           free         re   at    pi   po
   16     1     0  8081789  176008   19    5     6    7

 

You have very few Page Outs, you aren't short on memory during this time period.

 

Dave Olker
HPE Pro

Re: How to disable the filesystem cache on HP-UX 11i V1

Hi Narendra,

 

You can learn all about Direct I/O and how to enable it by reading the JFS Tuning white paper found here;

 

http://bizsupport2.austin.hp.com/bc/docs/support/SupportManual/c01919408/c01919408.pdf

 

The Direct I/O and CIO discussion begins on page 12. 

 

Regards,

 

Dave