From: Douglas Gilbert <dougg@torque.net>
To: Aboo Valappil <aboo@aboo.org>
Cc: linux-scsi@vger.kernel.org
Subject: Re: About SG Elements of request_buffer
Date: Sun, 15 Oct 2006 11:40:16 -0400 [thread overview]
Message-ID: <45325660.6070906@torque.net> (raw)
In-Reply-To: <453223AA.50409@aboo.org>
Aboo Valappil wrote:
> Hi All,
>
> Thanks for all your support for my previous posts.
>
> I have two questions.
>
> 1. Is it safe to assume that all the SG elements of request_buffer are
> page aligned? (Except the first one and last one), I mean, it is always
> multiple of pages?
>
> 2. What are situations reading a scsi disk (using dd ) cause a write to
> the disk? When I read my virtual scsi disk using dd command, block
> layer is generating lot of SCSI write, as well as reads. Any thoughts?
> Besides this observation, everything is working fine.
Aboo,
A comment on your second point: to bypass the vagaries of
the block layer caching with dd (or sg_dd) use 'iflag=direct'
and/or 'oflag=direct' as required. There may be alignment
constraints.
Doug Gilbert
next prev parent reply other threads:[~2006-10-15 15:38 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-10-15 12:03 About SG Elements of request_buffer Aboo Valappil
2006-10-15 15:40 ` Douglas Gilbert [this message]
2006-10-15 15:53 ` James Bottomley
2006-10-25 9:05 ` Aboo Valappil
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