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Re: What should be the value f_frsize if my db_block_size is 8Kb in oracle database

 
Ayaz Ahmad
Occasional Advisor

What should be the value f_frsize if my db_block_size is 8Kb in oracle database

We are having a performance issue, we suspect I/O bottleneck, can anybody help this may be because of our OS f_frsize is 1Kb and Database db_block_size is 8Kb
output below:
From OS:
fstyp -v /dev/vx/dsk/r1sp1dbdg/sapdata31
vxfs
version: 5
f_bsize: 8192
f_frsize: 1024

From Oracle Database:
DB_BLOCK_SIZE=8192

Please also clear what is the difference between f_bsize & f_frsize. My file system is vxfs.
OS-HPux version 11.23
DB- Oracle 9i

SAP recomendation regarding the above mentioned parameter of vxfs.
18 REPLIES 18
T G Manikandan
Honored Contributor

Re: What should be the value f_frsize if my db_block_size is 8Kb in oracle database

f_bsize block size (8K) largest possible block size (8K)
f_frsize fragment size (1K) actual block size (usually 1K)


So your filesystem is running with 1k blocksize. When you create the filesystem using newfs command you need to use -b to provide the blocksize.

You cannot change the block size of a filesystem without recreating it.

Re: What should be the value f_frsize if my db_block_size is 8Kb in oracle database

running fstyp for a VxFS filesystem can be a little confusing. In the case of VxFS its the f_frsize that represents the filesystem blocksize that you need to match against Oracle's block size.

You get a clearer indication from "mkfs -m"

mkfs -F vxfs -m /dev/vx/dsk/r1sp1dbdg/sapdata31

Don't worry, mkfs -m is non-destructive.

In your case it looks like you'll have to recreate your filesystem with the correct newfs options for a 8k blocksize

HTH

Duncan

I am an HPE Employee
Accept or Kudo
Ayaz Ahmad
Occasional Advisor

Re: What should be the value f_frsize if my db_block_size is 8Kb in oracle database

Thanks for the info.

But does it anyway may hamper io performance of the system.

What is the sap recomendation for block size of the vxfs file system where database files are residing.

I found a difference between db_block_size & f_frsize on my system. Is this setings creating the performance issue?
T G Manikandan
Honored Contributor

Re: What should be the value f_frsize if my db_block_size is 8Kb in oracle database

Yes definitely, but I dont have the stats with me for the percentage drop with performance.

Oracle recommends that your database block size be equal-match, or be multiples of your operating system block size.

1k to 8k is quite significant.

Re: What should be the value f_frsize if my db_block_size is 8Kb in oracle database

So as you are currently configured, every Oracle IO is going to generate 8 filesystem IOs - not ideal, but maybe not an issue depending on your IO load profile.

Re-creating the filesystems with 8K blocksize might help, or it might just slightly reduce the amount of SYS CPU time for Oracle processes, but it certainly won't make the situation worse.

Given that its a lot of work to do this (you have to newfs your filesystem so a full backup and restore will be required), you probably want to have some confidence that this is actually causing you a problem first.

Do you actually have a performance issue on this system?

HTH

Duncan

I am an HPE Employee
Accept or Kudo
Ayaz Ahmad
Occasional Advisor

Re: What should be the value f_frsize if my db_block_size is 8Kb in oracle database

Hi Duncan,

Yes, we are facing a major performance issue, sap team is telling Disk Average Write time on the system is very high, as per them system is taking 5ms for 8kb and 30ms for 64kb whereas it should take around 10-12 ms for 64kb instead. from OS perspective we get value of AVSERV within 6ms from sar -d output, AVWAIT is less than 0.5ms. I believe that AVSERV counts for both read/Write operation,
What is the way to find out average service time for Disk write operations only?

Re: What should be the value f_frsize if my db_block_size is 8Kb in oracle database

If you have measureware/performance agent you can pull out these stats by looking at the BYDSK_AVG_WRITE_SERVICE_TIME metric.

Do you have measureware/ovpa installed?

You can check using:

mwa status

if that comes back with something meaningful I can talk you through using measureware to get this data.

HTH

Duncan

I am an HPE Employee
Accept or Kudo
T G Manikandan
Honored Contributor

Re: What should be the value f_frsize if my db_block_size is 8Kb in oracle database

# time dd if=/dev/zero of=/testfile bs=1024k count=1024

This will provide you the write time into the disk for creating a 1G testfile.
Hein van den Heuvel
Honored Contributor

Re: What should be the value f_frsize if my db_block_size is 8Kb in oracle database

Is it not time to move forward to Oracle 10g first and foremost? The system is missing out on 5+ years of development!

IMHO the files system block size should be entirely irrelevant for a properly setup system using mount options mincache=direct and convosync=direct.

What is behind this sapdata31?
Your data is almost reasonable for a single direct connect disk. but typically it is NOT just a direct connect simple disk , but a lun on a controller with some level of writeback cache probably connect with a fibre.
When the latter operates under its limits, you should really expect WRITE IO times of 1 or 2 milliseconds for 64kb, not 10+, because the write will be to controller memory.
Of course there need to be enough real disks behind the lun to suck up the throughput requirements.
The reads will typically involve getting data of a spinning disks, so 5+ ms there is fine.

If the write are slow, then either the write back cache is not operational (check batteries!?) or under configured (MBs), or the load in MB/sec is sustained higher than the combined disks can comfortably handle.

Ask your storage specialist on their opinion on the situation: IO/Sec, MB/sec and (thus) KB/IO, Response times.

Regards,
Hein van den Heuvel ( at gmail dot com )
HvdH Performance Consulting