topic Re: How to disable the filesystem cache on HP-UX 11i V1 in Operating System - HP-UX

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

NarendraUttekar — Thu, 05 Jan 2012 07:15:11 GMT

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

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

pradeep m — Thu, 05 Jan 2012 11:32:35 GMT

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

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

NarendraUttekar — Fri, 06 Jan 2012 06:13:11 GMT

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

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

pradeep m — Fri, 06 Jan 2012 09:00:45 GMT

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.

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

Dennis Handly — Fri, 06 Jan 2012 16:35:12 GMT

>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.)

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

Dave Olker — Fri, 06 Jan 2012 17:43:24 GMT

> 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?

NarendraUttekar — Mon, 09 Jan 2012 09:57:05 GMT

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

NarendraUttekar — Mon, 09 Jan 2012 10:06:57 GMT

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

NarendraUttekar — Mon, 09 Jan 2012 11:59:38 GMT

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

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

Dennis Handly — Mon, 09 Jan 2012 20:57:10 GMT

>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.

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

Dave Olker — Fri, 18 Jun 2021 09:46:32 GMT

Hi Narendra,

You can learn all about Direct I/O and how to enable it by reading the JFS Tuning technical 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