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SubjectRe: [Patch] SCSI: Retrieve Cache Mode Using SG_ATA_16 if normal routine fails
From
2011/10/11 Amit Sahrawat <amit.sahrawat83@gmail.com>:
> On Tue, Oct 11, 2011 at 4:11 PM, Hannes Reinecke <hare@suse.de> wrote:
>> On 10/11/2011 10:26 AM, Amit Sahrawat wrote:
>>>
>>> SCSI: Retrieve Cache Mode Using SG_ATA_16 if normal routine fails
>>>
>>> It has been observed that a number of USB HDD's do not respond correctly
>>> to SCSI mode sense command(retrieve caching pages) which results in their
>>> Write Cache being discarded by queue requests i.e., WCE if left set to
>>> '0'(disabled). So, in order to identify the devices correctly - give it
>>> a last try using SG_ATA_16 after failure from normal routine.
>>>
>> I'd be _VERY_ cautious when trying something like this.
>>
>> ATA_16 is a rather recent command, and most older drives simply can't cope
>> with this. Instead they just kick the error handler and go offline
>> eventually.
> I tried with a number of USB HDD(around 6 with different
> manufacturer's, 1 USB SSD and pen drives) - they are responding
> correctly with this.
>>
>> Shouldn't we rather use a sensible default, ie assume WCE is enabled?
> If WCE is enabled by default - that will mark QUEUE ORDERING to
> QUEUE_ORDERED_DRAIN_FLUSH(Preflush-Postflush)(ie., flushing will occur
> for all the Mass Storage devices - which in turn will keep on calling
> SYNC_CACHE for these devices(which do not have write cache)) - ie., an
> extra overhead for the devices which do not have this routine(Pen
> drives being widely used among these)
> Is there any identification(unique information) for "older drives" ?
> Please share your opinion more.
I think that it is good approach. Have you tested journaling test on XFS ?
For example, while tiny several files is written, Is there corruption
fail when suddenly unplugging usb HDD ?
And you should check write performance.
If you change a little, It will be better~ let me check more.
>
>>
>> Cheers,
>>
>> Hannes
>> --
>> Dr. Hannes Reinecke                   zSeries & Storage
>> hare@suse.de                          +49 911 74053 688
>> SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
>> GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
>>
> Regards,
> Amit Sahrawat
>
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