Degrading performance?

Degrading performance?

[Bill Rees]

Hi,

I've got a appication I'm testing that writes millions
of 15K files to an 800gb raidset (5x160 gb Maxtor
drives on a 3ware 7450 controller).  The basic format
of the directory structure is as follows:

/partition/00/yyyymmdd/hhmm/file1 (15k)
/partition/00/yyyymmdd/hhmm/file2 (15k)
/partition/00/yyyymmdd/hhmm/file3 (15k)
.
.
.
/partition/00/yyyymmdd/hhmm/file1800 (15k)

Where yyyymmdd is a date and hhmm is a time.  My test
program simulates a production system.  I'm writing
1800 files filled with nulls as fast as my CPU will
allow for each subdirectory in an effort to fill the
raidset.

I compute the time in milliseconds that it takes to
fill a directory with the 1800 files.  As the disk
fills, the number of megabytes the application can
write per second gradually degrades from around 8.5
mb/sec when the disk is 2% full to 1.3 mb/sec at 23%
full.  I tried the same test on a single 160gb disk
and, although the performance was a bit better, the
degradation is still there.  A single 160gb formatted
with ext2 does not seem to show this gradual
degradation.

Does this sound like normal behavior and does anyone
have a suggestion on what could be done to optimize
this?  My production application can handle multiple
partitions so I could break up the 800gb raid.

Any help or suggestions would be appreciated.

Bill





=====
Bill Rees - bill@billrees.com - http://billrees.com

__________________________________________________
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Re: Degrading performance?

[Hans Reiser]

Bill Rees wrote:

>Hi,
>
>I've got a appication I'm testing that writes millions
>of 15K files to an 800gb raidset (5x160 gb Maxtor
>drives on a 3ware 7450 controller).  The basic format
>of the directory structure is as follows:
>
>/partition/00/yyyymmdd/hhmm/file1 (15k)
>/partition/00/yyyymmdd/hhmm/file2 (15k)
>/partition/00/yyyymmdd/hhmm/file3 (15k)
>.
>.
>.
>/partition/00/yyyymmdd/hhmm/file1800 (15k)
>
>Where yyyymmdd is a date and hhmm is a time.  My test
>program simulates a production system.  I'm writing
>1800 files filled with nulls as fast as my CPU will
>allow for each subdirectory in an effort to fill the
>raidset.
>
>I compute the time in milliseconds that it takes to
>fill a directory with the 1800 files.  As the disk
>fills, the number of megabytes the application can
>write per second gradually degrades from around 8.5
>mb/sec when the disk is 2% full to 1.3 mb/sec at 23%
>full.  I tried the same test on a single 160gb disk
>and, although the performance was a bit better, the
>degradation is still there.  A single 160gb formatted
>with ext2 does not seem to show this gradual
>degradation.
>
>Does this sound like normal behavior and does anyone
>have a suggestion on what could be done to optimize
>this?  My production application can handle multiple
>partitions so I could break up the 800gb raid.
>
>Any help or suggestions would be appreciated.
>
>Bill
>
>
>
>
>
>=====
>Bill Rees - bill@billrees.com - http://billrees.com
>
>__________________________________________________
>Do You Yahoo!?
>Yahoo! Tax Center - online filing with TurboTax
>http://taxes.yahoo.com/
>
>
This is a very interesting measurement.  Please experiment with the 
patch to bitmap.c that Oleg is experimenting with (I think it was put on 
the reiserfs mailing list recently).

I think you will find the various mount options of interest.

Hans

Re: Degrading performance?

[Oleg Drokin]

Hello!

On Wed, Apr 10, 2002 at 10:10:08PM +0400, Hans Reiser wrote:

> This is a very interesting measurement.  Please experiment with the 
> patch to bitmap.c that Oleg is experimenting with (I think it was put on 
> the reiserfs mailing list recently).

No, What I put on list is different stuff we was working on with Chris Mason.
Though it may also help.

Bye,
    Oleg

Re: Degrading performance?

[Hans Reiser]

Bill Rees wrote:

>Hi,
>
>I've got a appication I'm testing that writes millions
>of 15K files to an 800gb raidset (5x160 gb Maxtor
>drives on a 3ware 7450 controller).  The basic format
>of the directory structure is as follows:
>
>/partition/00/yyyymmdd/hhmm/file1 (15k)
>/partition/00/yyyymmdd/hhmm/file2 (15k)
>/partition/00/yyyymmdd/hhmm/file3 (15k)
>.
>.
>.
>/partition/00/yyyymmdd/hhmm/file1800 (15k)
>
>Where yyyymmdd is a date and hhmm is a time.  My test
>program simulates a production system.  I'm writing
>1800 files filled with nulls as fast as my CPU will
>allow for each subdirectory in an effort to fill the
>raidset.
>
>I compute the time in milliseconds that it takes to
>fill a directory with the 1800 files.  As the disk
>fills, the number of megabytes the application can
>write per second gradually degrades from around 8.5
>mb/sec when the disk is 2% full to 1.3 mb/sec at 23%
>full.  I tried the same test on a single 160gb disk
>and, although the performance was a bit better, the
>degradation is still there.  A single 160gb formatted
>with ext2 does not seem to show this gradual
>degradation.
>
>Does this sound like normal behavior and does anyone
>have a suggestion on what could be done to optimize
>this?  My production application can handle multiple
>partitions so I could break up the 800gb raid.
>
>Any help or suggestions would be appreciated.
>
>Bill
>
>
>
>
>
>=====
>Bill Rees - bill@billrees.com - http://billrees.com
>
>__________________________________________________
>Do You Yahoo!?
>Yahoo! Tax Center - online filing with TurboTax
>http://taxes.yahoo.com/
>
>
Oleg, try to replicate his result, and ask him for the program.

Hans

Re: Degrading performance?

[Oleg Drokin]

Hello!

On Wed, Apr 10, 2002 at 10:25:02AM -0700, Bill Rees wrote:

> fills, the number of megabytes the application can
> write per second gradually degrades from around 8.5
> mb/sec when the disk is 2% full to 1.3 mb/sec at 23%

What kernel version are you using?

Bye,
    Oleg