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Re: What`s wrong with JFS configuration?

From: Jim Nasby <decibel(at)decibel(dot)org>
To: Paweł Gruszczyński <pawel(dot)gruszczynski(at)inea(dot)com(dot)pl>
Cc: Postgresql Performance list <pgsql-performance(at)postgresql(dot)org>
Subject: Re: What`s wrong with JFS configuration?
Date: 2007-04-27 14:08:50
Message-ID: 674CBCD3-C886-4723-8F6D-702E359C66B8@decibel.org (view raw or flat)
Thread:
Lists: pgsql-performance
Adding -performance back in so others can learn.

On Apr 26, 2007, at 9:40 AM, Paweł Gruszczyński wrote:

> Jim Nasby napisał(a):
>> On Apr 25, 2007, at 8:51 AM, Paweł Gruszczyński wrote:
>>> where u6 stores Fedora Core 6 operating system, and u0 stores 3  
>>> partitions with ext2, ext3 and jfs filesystem.
>>
>> Keep in mind that drives have a faster data transfer rate at the  
>> outer-edge than they do at the inner edge, so if you've got all 3  
>> filesystems sitting on that array at the same time it's not a fair  
>> test. I heard numbers on the impact of this a *long* time ago and  
>> I think it was in the 10% range, but I could be remembering wrong.
>>
>> You'll need to drop each filesystem and create the next one go get  
>> a fair comparison.
>
> I thought about it by my situation is not so clear, becouse my hard  
> drive for postgresql data is rather "logical" becouse of RAID array  
> i mode 1+0. My RAID Array is divided like this:
>
>   Device Boot      Start         End      Blocks   Id  System
> /dev/sda1               1      159850   163686384   83  Linux
> /dev/sda2          159851      319431   163410944   83  Linux
> /dev/sda3          319432      478742   163134464   83  Linux
>
> and partitions are:
>
> /dev/sda1     ext2   161117780   5781744 147151720   4% /fs/ext2
> /dev/sda2     ext3   160846452   2147848 150528060   2% /fs/ext3
> /dev/sda3      jfs   163096512   3913252 159183260   3% /fs/jfs
>
> so if RAID 1+0 do not change enything, JFS file system is at third  
> partition wich is at the end of hard drive.

Yes, which means that JFS is going to be at a disadvantage to ext3,  
which will be at a disadvantage to ext2. You should really re-perform  
the tests with each filesystem in the same location.

> What about HDD with two magnetic disk`s? Then the speed depending  
> of partition phisical location is more difficult to calculate ;)  
> Propably first is slow, secund is fast in firs halt and slow in  
> secund halt, third is the fastes one. In both cases my JFS partitin  
> should be ath the end on magnetic disk. Am I wrong?

I'm not a HDD expert, but as far as I know the number of platters  
doesn't change anything. When you have multiple platters, the drive  
essentially splits bytes across all the platters; it doesn't start  
writing one platter, then switch to another platter.
--
Jim Nasby                                            jim(at)nasby(dot)net
EnterpriseDB      http://enterprisedb.com      512.569.9461 (cell)



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