From: Ric Wheeler <rwheeler@redhat.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: linux-fsdevel@vger.kernel.org
Subject: Re: USB storage & write barrier support?
Date: Mon, 23 Nov 2009 15:46:03 -0500 [thread overview]
Message-ID: <4B0AF48B.1090904@redhat.com> (raw)
In-Reply-To: <Pine.LNX.4.44L0.0911231534420.2958-100000@iolanthe.rowland.org>
On 11/23/2009 03:37 PM, Alan Stern wrote:
> On Mon, 23 Nov 2009, Ric Wheeler wrote:
>
>> Hi Alan,
>>
>> One quick question - how robust is our support for write barriers over USB?
>>
>> Specifically, I am looking to get together some testing with both
>> external USB and e-sata enclosure for various file systems and would be
>> very interested in helping make sure that this is well handled...
>
> It's extremely robust -- the USB mass-storage driver has a maximum
> command-queue length of 1!
>
> With the coming of USB 3.0 and the UASP (USB-Attached SCSI Protocol)
> specification this will change. I presume barriers will then be
> implemented as the need arises.
>
> Alan
>
What we need is to pass down cache flush commands (ATA_CACHE_FLUSH_EXT is what
flushed the cache for ATA/S-ATA devices). Even with a command-queue length of 1,
the write cache a USB connected s-ata drive would still loose data on power off
without this kind of support.
Ric
next prev parent reply other threads:[~2009-11-23 20:41 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-11-23 20:12 USB storage & write barrier support? Ric Wheeler
2009-11-23 20:37 ` Alan Stern
2009-11-23 20:46 ` Ric Wheeler [this message]
2009-11-23 20:49 ` Alan Stern
2009-11-23 20:57 ` Ric Wheeler
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