This message is from the T13 list server.
My (humble?) opinion is that FUA is necessary and is not dangerous as long as a disk
drive properly deals with outstanding requests.
First off a flush is very slow, affecting system benchmark scores by as much as 5%.
The more interesting fact is that not all drives properly support flush, where many
HDD's will complete the Flush command without writing any cached data to media just
because of the desire to make ones disk synthetically faster than somebody elses.
FUA allows the OS to flush critical data without adversely affecting performance. The
drive should be required to test all outstanding writes (in the queued case) and
assure that the writes are ordered to guarantee no data loss. Lets take a look at a
specific scenario:
- Queued write 256 sectors to LBA 10000
- FUA write 1 sector 10001
The 256-sector write must be written to media, or the 1 sector must over-write the
same sector written by the 256 sector write in the devices cache. The drive must also
assure that the media results in the same data. I'm sure we could expand this simple
case to something much more complex, but the basic idea remains: The drive must
handle ordering such that there is no data loss. I've asked once before, and I'll ask
it again: someone offer up a more complex scenario where you believe FUA will break
and we can then have a real conversation about the (de)merits of FUA.
MKE.
-----Original Message-----
From: Harlan Andrews [mailto:[EMAIL PROTECTED]
Sent: Friday, June 20, 2003 4:47 PM
To: Andre Hedrick; Steve Livaccari
Cc: Curtis Stevens; T13 List Server; [EMAIL PROTECTED]; Larry Barras
Subject: Re: [t13] hmmm.. no comments?
This message is from the T13 list server.
I have not been present at any of the discussions, but Out-Of-Order
writes are inherently dangerous to ANY file system - not only to
journaling. Now that we have Flush Cache as a mandatory command, why
don't we simply issue the Flush Cache to force unit access.
I have not heard any real benefit for such a dangerous operation. Why
would anyone even consider it ?
...Harlan
on 6/19/03 10:49 PM, [EMAIL PROTECTED] wrote:
>This message is from the T13 list server.
>
>
>
>Steve,
>
>This totally nukes and destroys write ordered operations.
>Example is the down/commit block on a journalled operation.
>
>Taking an FUA command to platter and blasting past the queue cache will
>destroy every bit of the security designed into any journaling file
>system.
>
>I still do not get why MicroSoft thinks there journaling NTFS of the
>meta data in OS buffer cache will not take a hit. If I knew the OS my
>data was dependent on did such a "FOOLISH" operation I would find another.
>
>If T13 continues to move towards making it possible for the HOST to do bad
>things, then the DEVICE is even worse.
>
>We can all pack our bags and go home and switch to T10, because nobody
>will trust a device coming out of T13 again.
>
>Comments?
>
>Tomato Shield UP!!
>
>Andre Hedrick
>LAD Storage Consulting Group
>
>On Wed, 18 Jun 2003, Steve Livaccari wrote:
>
>> This message is from the T13 list server.
>>
>>
>>
>> All modern HDD's have a buffer for write cache that is used to stack up
>> write data from both queued and unqueued write commands. A write command
>> followed by a flush cache command will likely not move the data from the
>> last write command to the media until the rest of the data is the write
>> cache is written. If a write FUA command is used the data from the write
>> FUA command will be given priority over the other data in the write cache
>> and be written first.
>>
>>
>>
>> Regards,
>> Steve Livaccari
>>
>> Hard Drive Engineering
>> IBM Global Procurement
>> Internet: [EMAIL PROTECTED]
>> Phone (919) 543.7393
>>
>>
>>
>
>> "Curtis Stevens"
>
>> <[EMAIL PROTECTED] To: "T13 List Server"
><[EMAIL PROTECTED]>
>> oo.com> cc:
>
>> Sent by: Subject: Re: [t13] hmmm..
no
>comments?
>> [EMAIL PROTECTED]
>
>> rg
>
>>
>
>>
>
>> 06/17/2003 11:09
>
>> PM
>
>>
>
>>
>
>>
>>
>>
>>
>> This message is from the T13 list server.
>>
>>
>> Gary
>>
>> As I recall, there were some inacuracies in the proposals as made to
>> the
>> committee. There were many revisions. The only new FUA commands that make
>> sense are the queued ones. All others could be followed by flush cache.
>>
>> ---------------------------
>> Curtis E. Stevens
>> 29 Dewey
>> Irvine, Ca 92620
>>
>> Home: (949) 552-4777
>> E-Mail: [EMAIL PROTECTED]
>>
>> The face of a child can say it all, especially the mouth part of the
>> face...
>> ----- Original Message -----
>> From: "Gary Laatsch" <[EMAIL PROTECTED]>
>> To: "Curtis Stevens" <[EMAIL PROTECTED]>; "T13 List Server"
>> <[EMAIL PROTECTED]>
>> Sent: Tuesday, June 17, 2003 4:40 PM
>> Subject: Re: [t13] hmmm.. no comments?
>>
>>
>> > Curtis and Hale,
>> >
>> > Also, to expand upon this. I think Hale's point is the proposal put
>> > forth by Nita didn't contain the QUEUE FUA or QUEUE FUA EXT commands and
>> he
>> > was wondering where they were added or how they were proposed. My memory
>> was
>> > this was discussed and added at the June 2002 meetings. That is why I
>> was
>> > wondering if anyone else remembered these discussions. I remember
>> > discussing all of this stuff (even Andre's comments about the FUA blowig
>> > away the queue) but for some reason it just wasn't captured very well in
>> the
>> > minutes.
>> >
>> > Gary Laatsch
>> > [EMAIL PROTECTED]
>> >
>> > ----- Original Message -----
>> > From: "Curtis Stevens" <[EMAIL PROTECTED]>
>> > To: "T13 List Server" <[EMAIL PROTECTED]>
>> > Sent: Tuesday, June 17, 2003 3:15 PM
>> > Subject: Re: [t13] hmmm.. no comments?
>> >
>> >
>> > > This message is from the T13 list server.
>> > >
>> > >
>> > > Hale
>> > >
>> > > I was there during the discussions and there was no secret
>> committee.
>> > > Basically, MS stated that they wanted to force meta data to the drive
>> > > without blowing the que. This means that although it is possible to
>> lose
>> > > data, in their application data loss would not occur...
>> > >
>> > > ---------------------------
>> > > Curtis E. Stevens
>> > > 29 Dewey
>> > > Irvine, Ca 92620
>> > >
>> > > Home: (949) 552-4777
>> > > E-Mail: [EMAIL PROTECTED]
>> > >
>> > > The face of a child can say it all, especially the mouth part of the
>> > face...
>> > > ----- Original Message -----
>> > > From: "Hale Landis" <[EMAIL PROTECTED]>
>> > > To: "T13 List Server" <[EMAIL PROTECTED]>
>> > > Sent: Tuesday, June 17, 2003 10:57 AM
>> > > Subject: [t13] hmmm.. no comments?
>> > >
>> > >
>> > > > This message is from the T13 list server.
>> > > >
>> > > >
>> > > > I'm curious why there are no comments about the question of the
>> > > > origin of the WRITE DMA QUEUED FUA command (where is the proposal?).
>> > > > And why no comments on QUEUED EXT commands with large sector counts.
>> > > >
>> > > > Is this because all these discussions must take place via the "secret
>> > > > society"?
>> > > >
>> > > > Hale
>> > > >
>> > > >
>> > > >
>> > > > *** Hale Landis *** www.ata-atapi.com ***
>> > > >
>> > > >
>> > >
>>
>>
>>
>>
>>
>
