All of lore.kernel.org
 help / color / mirror / Atom feed
From: Kai Makisara <Kai.Makisara@kolumbus.fi>
To: "Desai, Kashyap" <Kashyap.Desai@lsi.com>
Cc: Lukas Kolbe <lkolbe@techfak.uni-bielefeld.de>,
	Boaz Harrosh <bharrosh@panasas.com>,
	"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>
Subject: RE: After memory pressure: can't read from tape anymore
Date: Thu, 2 Dec 2010 22:25:14 +0200 (EET)	[thread overview]
Message-ID: <alpine.LNX.2.00.1012022215060.9213@kai.makisara.local> (raw)
In-Reply-To: <B2FD678A64EAAD45B089B123FDFC3ED709113B13@inbmail01.lsi.com>

On Thu, 2 Dec 2010, Desai, Kashyap wrote:

> 
> 
> > -----Original Message-----
> > From: Kai Makisara [mailto:Kai.Makisara@kolumbus.fi]
...
> > You can't convert write of one block into multiple IOs. If someone
> > wants
> > to write 2 MB blocks, the system must transfer 2 MB in one IO. The
> > choices
> > are:
> 
> I am not sure why single IO cannot be converted into multiple "IO" request.
> If you run below commands
> " sg_dd if=/dev/zero of=/dev/sdb bs=4800000 count=1"
> 
> You will see multiple IOs(requests) are coming to low layer driver. 
> 
Yes, but each one is writing one or more disk blocks of 512 bytes. You 
don't see writes of partial blocks. If the block size of the device is
2  MB, the minimun IO request is 2 MB. (The SCSI commands for sequential 
access devices are different from the commands for block devices, but the 
minimum read/write unit is one block in both cases.)

Kai

P.S. Why is it necessary to use 2 MB blocks? Some people say that it is 
the optimal block size for some current tape drives.

  reply	other threads:[~2010-12-02 20:25 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-11-28 19:15 After memory pressure: can't read from tape anymore Lukas Kolbe
2010-11-29 17:09 ` Kai Makisara
2010-11-30 13:31   ` Lukas Kolbe
2010-11-30 16:10     ` Boaz Harrosh
2010-11-30 16:23       ` Kai Makisara
2010-11-30 16:44         ` Boaz Harrosh
2010-11-30 17:04           ` Kai Makisara
2010-11-30 17:24             ` Boaz Harrosh
2010-11-30 19:53               ` Kai Makisara
2010-12-01  9:40                 ` Lukas Kolbe
2010-12-02 11:17                   ` Desai, Kashyap
2010-12-02 16:22                     ` Kai Makisara
2010-12-02 18:14                       ` Desai, Kashyap
2010-12-02 20:25                         ` Kai Makisara [this message]
2010-12-05 10:44                           ` Lukas Kolbe
2010-12-03 10:13                       ` FUJITA Tomonori
2010-12-03 10:45                         ` Desai, Kashyap
2010-12-03 11:11                           ` FUJITA Tomonori
2010-12-02 10:01                 ` Lukas Kolbe
2010-12-03  9:44               ` FUJITA Tomonori
2010-11-30 16:20     ` Kai Makisara
2010-12-01 17:06       ` Lukas Kolbe
2010-12-02 16:41         ` Kai Makisara
2010-12-06  7:59           ` Kai Makisara
2010-12-06  8:50             ` FUJITA Tomonori
2010-12-06  9:36             ` Lukas Kolbe
2010-12-06 11:34               ` Bjørn Mork
2010-12-08 14:19               ` Lukas Kolbe
2010-12-03 12:27   ` FUJITA Tomonori
2010-12-03 14:59     ` Kai Mäkisara
2010-12-03 15:06       ` James Bottomley
2010-12-03 17:03         ` Lukas Kolbe
2010-12-03 18:10           ` James Bottomley
2010-12-05 10:53             ` Lukas Kolbe
2010-12-05 12:16               ` FUJITA Tomonori
2010-12-14 20:35             ` Vladislav Bolkhovitin
2010-12-14 22:23               ` Stephen Hemminger
2010-12-15 16:27                 ` Vladislav Bolkhovitin

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=alpine.LNX.2.00.1012022215060.9213@kai.makisara.local \
    --to=kai.makisara@kolumbus.fi \
    --cc=Kashyap.Desai@lsi.com \
    --cc=bharrosh@panasas.com \
    --cc=linux-scsi@vger.kernel.org \
    --cc=lkolbe@techfak.uni-bielefeld.de \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.