Re: [PATCH] USB: storage: add "no SYNCHRONIZE CACHE" quirk

From: Stefan Richter <stefanr-MtYdepGKPcBMYopoZt5u/LNAH6kLmebB@public.gmane.org>
To: James Bottomley
	<James.Bottomley-d9PhHud1JfjCXq6kfMZ53/egYHeGw8Jk@public.gmane.org>
Cc: Alan Stern
	<stern-nwvwT67g6+6dFdvTe/nMLpVzexx5G7lz@public.gmane.org>,
	Greg KH <greg-U8xfFu+wG4EAvxtiuMwx3w@public.gmane.org>,
	James Bottomley
	<JBottomley-MU7nAjRaF3makBO8gow8eQ@public.gmane.org>,
	Jun Itou <itou_jun-6LX5ZuzTTw53+QwDJ9on6Q@public.gmane.org>,
	Markus Rathgeb
	<maggu2810-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	Matt <vickm78-PkbjNfxxIARBDgjK7y7TUQ@public.gmane.org>,
	SCSI development list
	<linux-scsi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	USB Storage list
	<usb-storage-ijkIwGHArpdIPJnuZ7Njw4oP9KaGy4wf@public.gmane.org>,
	USB list <linux-usb-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	Jens Axboe <axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org>
Subject: Re: [PATCH] USB: storage: add "no SYNCHRONIZE CACHE" quirk
Date: Fri, 26 Jun 2015 11:43:08 +0200	[thread overview]
Message-ID: <20150626114308.7b5b8006@kant> (raw)
In-Reply-To: <1434994588.2237.90.camel-d9PhHud1JfjCXq6kfMZ53/egYHeGw8Jk@public.gmane.org>

On Jun 22 James Bottomley wrote:
> On Mon, 2015-06-22 at 13:30 -0400, Alan Stern wrote:
> > On Mon, 22 Jun 2015, James Bottomley wrote:
> > > Obviously, for a disk with a writeback cache that can't do flush, that
> > > window is much wider and the real solution should be to try to switch
> > > the cache to write through.
> > 
> > I agree.  Doing the switch manually (by writing to the "cache_type" 
> > attribute file) works, but it's a nuisance to do this when you have a 
> > portable USB drive that gets moved among a bunch of machines.
> 
> Perhaps it might be wise to do this to every USB device ... for external
> devices, the small performance gain doesn't really make up for the
> potential data loss.

Just a small note on the assumption of externally (and in extension,
temporarily) attached devices:  Not all USB-attached devices are external,
and not all external devices are used as removable devices.

(For example, I am using 2 internal CD-ROMs via USB-2 + usb-storage and 2
internal HDDs via USB 3 + uas in a PC with too few SATA ports and no PCIe
slot to spare for a controller add-on card, but plenty of USB headers
available on the mainboard.  Similarly, some NASes have their operating
system located on a USB-attached device.  Small offices use USB-attached
disks for backup and won't detach such a disk until rotation for off-site
deposit.  Not to mention embedded computers with USB-attached but fixed
disks.)
-- 
Stefan Richter
-=====-===== -==- ==-=-
http://arcgraph.de/sr/
--
To unsubscribe from this list: send the line "unsubscribe linux-usb" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html