RE: File system performance, hardware performance, ext3, 3ware RA ID1, etc.

RE: File system performance, hardware performance, ext3, 3ware RA ID1, etc.

[Adam Radford]

Perhaps you are issuing non purely sequential IO.  The card firmware does
some 
reodering, but at some point it will cause performance degradation.  Can you
try 
kernel 2.6 w/xfs? 

Also, in my experience, the 'raw io' interface doesn't issue any
asynchronous IO.  The
card _definately_ needs asynchronous IO posted to it or you will not get
good results
because you won't get all the drives busy.

-Adam

-----Original Message-----
From: Timothy Miller [mailto:miller@techsource.com]
Sent: Friday, February 13, 2004 2:57 PM
To: Daniel Blueman
Cc: linux-kernel@vger.kernel.org
Subject: Re: File system performance, hardware performance, ext3, 3ware
RAID1, etc.




Daniel Blueman wrote:
> Willy Tarreau <willy@w.ods.org> wrote in message
> news:<1oEGw-2ex-1@gated-at.bofh.it>...
> 
>>On Thu, Feb 12, 2004 at 06:32:31PM -0500, Timothy Miller wrote:
>> 
>>
>>>For writes, iozone found an upper bound of about 10megs/sec, which is 
>>>abysmal.  Typically, I'd expect writes to be faster (on a single drive) 
>>>than reads, because once the write is sent, you can forget about it. 
>>>You don't have to wait around for something to come back, and that 
>>>latency for reads can hurt performance.  The OS can also buffer writes 
>>>and reorder them in order to improve efficiency.
>>
>>It depends on the disk too. Lots of disks (specially IDE) are far slower
>>on writes than they are on reads.
> 
> 
> No. Have you verified this? If you 'dd' your swap partition from /dev/zero
> on IDE, you'll see write performance closely matches read performance, for
> drives old and new.
> 

And this sort of things is what I find with raw writes to the model of 
drive I'm using.  However, it seems that there must be some issue with 
the 3ware 7000-2 which is killing performance, or the way the Linux 
kernel is dealing with this sorta-SCSI device.

The WD1200JB should get like 30-40 megs/sec, but when being accessed 
through the 3ware, I get 10-16 megs/sec.

What could the 3ware be doing?

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Re: File system performance, hardware performance, ext3, 3ware RA ID1, etc.

[Timothy Miller]

Adam Radford wrote:
> Perhaps you are issuing non purely sequential IO.  The card firmware does
> some 
> reodering, but at some point it will cause performance degradation.  Can you
> try 
> kernel 2.6 w/xfs? 

Not any time soon, but as I mentioned earlier, I measured 13.9 megs/sec 
when I ran this command:

     time dd if=/dev/zero of=/dev/sda2 bs=1024k count=1024

No file system was involved; I was simply writing zeros to the block 
device (swap partition with swap off).  It took 73.522 seconds to do the 
above operation.  Also, I was running in single-user mode while doing 
the test.

> 
> Also, in my experience, the 'raw io' interface doesn't issue any
> asynchronous IO.  The
> card _definately_ needs asynchronous IO posted to it or you will not get
> good results
> because you won't get all the drives busy.

With RAID1, both drives will be written with the same data.  There is no 
need to be asynchronous, since it's all completely linear and sequential 
with large data blocks.

Re: File system performance, hardware performance, ext3, 3ware RA ID1, etc.

[Daniel Blueman]

Tim,

Do you get the same numbers (but slightly higher, as this is will measure
from a smaller portion of outer zones) with:

# hdparm -t /dev/sda

?

> Adam Radford wrote:
> > Perhaps you are issuing non purely sequential IO.  The card firmware
> does
> > some 
> > reodering, but at some point it will cause performance degradation.  Can
> you
> > try 
> > kernel 2.6 w/xfs? 
> 
> Not any time soon, but as I mentioned earlier, I measured 13.9 megs/sec 
> when I ran this command:
> 
>      time dd if=/dev/zero of=/dev/sda2 bs=1024k count=1024
> 
> No file system was involved; I was simply writing zeros to the block 
> device (swap partition with swap off).  It took 73.522 seconds to do the 
> above operation.  Also, I was running in single-user mode while doing 
> the test.
> 
> > 
> > Also, in my experience, the 'raw io' interface doesn't issue any
> > asynchronous IO.  The
> > card _definately_ needs asynchronous IO posted to it or you will not get
> > good results
> > because you won't get all the drives busy.
> 
> With RAID1, both drives will be written with the same data.  There is no 
> need to be asynchronous, since it's all completely linear and sequential 
> with large data blocks.

-- 
Daniel J Blueman

GMX ProMail (250 MB Mailbox, 50 FreeSMS, Virenschutz, 2,99 EUR/Monat...)
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Re: File system performance, hardware performance, ext3, 3ware RA ID1, etc.

[Timothy Miller]

Daniel Blueman wrote:
> Tim,
> 
> Do you get the same numbers (but slightly higher, as this is will measure
> from a smaller portion of outer zones) with:
> 
> # hdparm -t /dev/sda
> 
> ?

I ran this test.  This is a read test.  What I did below was a write test.

Additionally, I ran this test:
     time dd if=/dev/sda of=/dev/null bs=1024k count=1024

 From that, I got 47 megs/sec.  From 'hdparm -t /dev/sda', I got a 
slightly lower number.

So, for reads, I'm getting good performance.  47 megs/sec at the 
outer-most tracks is a bit lower than the 50+ that reviewers report, but 
it's not bad.

However, I don't get anywhere near the 40+ megs/sec the reviewers say 
the drive gets for writes.  That model as a single drive in my wife's 
computer gets about 39 megs/sec, which is great.  But behind the 3ware, 
the drive gets only 13 megs/sec.  (iozone reports about 15 megs/sec, but 
that's influenced by caching in RAM, and iozone is writing to a file on 
tracks further out, I think.)

> 
> 
>>Adam Radford wrote:
>>
>>>Perhaps you are issuing non purely sequential IO.  The card firmware
>>
>>does
>>
>>>some 
>>>reodering, but at some point it will cause performance degradation.  Can
>>
>>you
>>
>>>try 
>>>kernel 2.6 w/xfs? 
>>
>>Not any time soon, but as I mentioned earlier, I measured 13.9 megs/sec 
>>when I ran this command:
>>
>>     time dd if=/dev/zero of=/dev/sda2 bs=1024k count=1024
>>
>>No file system was involved; I was simply writing zeros to the block 
>>device (swap partition with swap off).  It took 73.522 seconds to do the 
>>above operation.  Also, I was running in single-user mode while doing 
>>the test.
>>
>>
>>>Also, in my experience, the 'raw io' interface doesn't issue any
>>>asynchronous IO.  The
>>>card _definately_ needs asynchronous IO posted to it or you will not get
>>>good results
>>>because you won't get all the drives busy.
>>
>>With RAID1, both drives will be written with the same data.  There is no 
>>need to be asynchronous, since it's all completely linear and sequential 
>>with large data blocks.
> 
>