linux-ext4 - Re: problem(?) in ext4 or mke2fs

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Date:	Sun, 3 Apr 2011 14:50:18 -1000
From:	Andreas Dilger <adilger@...mcloud.com>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	Zeev Tarantov <zeev.tarantov@...il.com>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: problem(?) in ext4 or mke2fs

Sorry for the previous empty message...

I was just going to write that it makes sense to have mballoc use a reasonably large stripe size (e.g. 1MB) that is an even multiple of the underlying device blocksize. 

Something like the following might work:

  if (ioopt != 0)
    stripe = max(1, (1048576 + ioopt - 1) / ioopt) * ioopt;
  else
    stripe = 0;

And let the kernel decide what to do if unspecified. I'd prefer to leave it unset if there is nothing provided by the device, so we don't confuse the default value with a value specified by the admin. 

Cheers, Andreas

On 2011-04-03, at 8:56 AM, Eric Sandeen <sandeen@...hat.com> wrote:

> On 4/3/11 11:52 AM, Zeev Tarantov wrote:
>> On Sun, Apr 3, 2011 at 21:40, Eric Sandeen <sandeen@...hat.com> wrote:
> 
> ...
> 
>>> What does
>>> 
>>> # blockdev --getiomin --getioopt /dev/<yourdevice>
>>> 
>>> say for your device?
>> 
>> get logical block (sector) size: 4096
>> get physical block (sector) size: 4096
>> get minimum I/O size: 4096
>> get optimal I/O size: 4096
>> get alignment offset in bytes: 0
>> get max sectors per request: 255
>> get blocksize: 4096
>> get readahead: 256
>> 
>>> The device may be reporting odd values, but mke2fs probably
>>> should be smart enough not to set block-sized stripe unit and width...
>> 
>> If the filesystem created with the default options is slow or has
>> higher cpu usage, it should be changed.
> 
> I agree.  For actual striped storage, this makes it faster, but this
> case is a problem; block-sized stripe width is never going to be good.
> What device is this, exactly?
> 
> -Eric (losing my free airport wifi in about 8 minutes, so I may have
> to continue this later...!)
> 
>>> -Eric
>> 
>> -Z.T.
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