From mboxrd@z Thu Jan  1 00:00:00 1970
From: Lars Melin <larsm17@gmail.com>
Subject: Re: dummy scsi read or scsi command periodically for external USB
 Hard Disk
Date: Mon, 07 Jul 2014 21:59:43 +0700
Message-ID: <53BAB5DF.5090606@gmail.com>
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To: loody <miloody@gmail.com>, "Bryn M. Reeves" <bmr@redhat.com>
Cc: "linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>, SCSI development list <linux-scsi@vger.kernel.org>

On 2014-07-07 21:37, loody wrote:
> hi Bryn:
>
> 2014-07-07 17:20 GMT+08:00 Bryn M. Reeves <bmr@redhat.com>:
>> On Sun, Jul 06, 2014 at 01:18:03AM +0800, loody wrote:
>>> hi all:
>>>      we met a USB Hard Disk that will go to suspend if host stop
>>> sending scsi command over 5mins.
>>>      To save the IO, kernel will keep the file in page cache as much as
>>> he can and under this circumstances, the scsi command may disappear
>>> for a while longer enough to cause the device suspend.
>>>
>>>      is there any kernel config or module parameter can do the dummy
>>> read or scsi command periodically?
>> No but you could set up a simple cron job to call an sg3_utils command.
>>
>> E.g. issue an sg_read for one sector to the device every 4m:
>>
>>    */4 * * * * sg_read count=1 if=/dev/<disk>
> Since my target platform arm embedded system,
> does that mean I should include sg_read in my Busybox
> or
> cross-compile sg_read from sg3_utils?
>
> appreciate your kind help,
> --
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sgread is not included in BusyBox but you should have "touch".
Create a dummy file on the disk and let cron touch it every 4 minutes.