From: ching <[email protected]>
To: Josef Bacik <[email protected]>
Cc: "[email protected]" <[email protected]>
Subject: Re: ssd alignment and btrfs sector size
Date: Fri, 14 Sep 2012 07:45:17 +0800 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
On 09/13/2012 09:00 PM, Josef Bacik wrote:
> On Thu, Sep 13, 2012 at 12:02:04AM -0600, ching lu wrote:
>> I am trying to test btrfs on my ssd, i am studying about btrfs and alignment.
>>
>> I have read this old mail:
>> http://www.mail-archive.com/[email protected]/msg16177.html
>>
>> According to the thread, 3 parameters should be tuned
>>
>> 1. leafsize
>> 2. nodesize
>> 3. sectorsize
>>
>> The first two parameters are easy to understand, but how does
>> "sectorsize" affect the alignment?
>>
>> If the erase block size of my SSD is 16k, and i set
>> leafsize=nodesize=16k, leave the sectorsize=4k (default), will it
>> causes misalignment?
> So frist leafsize/nodesize will always be the same, so if you set one to 16k
> mkfs will autmatically set the other to 16k, it's just way back when we had
> grand plans of having different sizes for both.
>
> Secondly your erase block size is 16k? What kind of drive are you using? But
> yeah 4k sectorsize will result in misaligned writes to the data area, but your
> metadata will be aligned. Hopefully the raid5/6 code will be out soon and we'll
> be able to do > page size sectorsize and you'll be able to set
> leafsize==sectorsize. Btw most normal SSDs have waaaay larger erase blocks, on
> the order of several MB, so it's not the worst thing to write to the middle of
> erase blocks, everybody does it anyway. Thanks,
>
> Josef
>
16k is just a assumption only, thanks for your help anyway.
prev parent reply other threads:[~2012-09-13 23:45 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-13 6:02 ssd alignment and btrfs sector size ching lu
2012-09-13 13:00 ` Josef Bacik
2012-09-13 23:45 ` ching [this message]
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