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From: Wout Mertens <wmertens@cisco.com>
To: Magicloud Magiclouds <magicloud.magiclouds@gmail.com>
Cc: linux-btrfs@vger.kernel.org
Subject: Re: Interesting problem with write data.
Date: Thu, 18 Nov 2010 11:36:34 +0100	[thread overview]
Message-ID: <70DF2C9D-0157-4FCB-B1AF-8A84E017249C@cisco.com> (raw)
In-Reply-To: <AANLkTinTtvN6T6Ykjs6-UzHi3XYgimM92Pa5wSPrF3sZ@mail.gmail.com>

I think test 2 actually makes dd allocate 1GB of memory and then write it to disk. So if you don't have 1GB free you may be testing your swap.

Also, what kernel/btrfs version are you using? In what situations are you experiencing slowness?

Wout.

On Nov 18, 2010, at 7:19 , Magicloud Magiclouds wrote:

> Hi,
>  Recently, I made a btrfs to use. And I met slowness problem. Trying
> to diag it. I found this:
> 1. dd if=/dev/zero of=test count=1024 bs=1MB
> This is fast, at about 25MB/s, and reasonable iowait.
> 2. dd if=/dev/zero of=test count=1 bs=1GB
> This is pretty slow, at about 1.5MB/s, and 90%+ iowait, constantly.
>  May I know why it works like this? Thanks.
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 


  reply	other threads:[~2010-11-18 10:36 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-11-18  6:19 Interesting problem with write data Magicloud Magiclouds
2010-11-18 10:36 ` Wout Mertens [this message]
2010-11-18 12:03 Tomasz Chmielewski
2010-11-18 14:23 ` Chris Mason
2010-11-18 14:57   ` Tomasz Chmielewski
2010-11-18 15:07     ` Chris Mason
2010-11-18 15:39       ` Tomasz Chmielewski
2010-11-18 15:54         ` Chris Mason
2010-11-18 16:00           ` Tomasz Chmielewski
2010-11-18 16:07             ` Chris Mason

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