Hugh,
There seems to be some confusion about how FUA works.
Some people seem to think that FUA requests get promoted in the queue.
Others (myself included) believe that FUA should simply delay return until that request AND ALL other requests ahead of it in the queue have been flushed to the media.
I believe the drive MUST maintain data integrity even if the write commands do overlap in the queue.
...Harlan
On Monday, June 23, 2003, at 4:02 PM, Hugh Curley wrote:
This message is from the T13 list server.
Someone requested the FUA command for a specific purpose. That purpose is
to immediately execute the write without the performance hit of a flush
cache. That is the way the command should work. Any driver writer that
issues the FUA command with overlapping reads already in the queue deserves
what will happen.
The command was requested for an operation that will not include overlap
data.
I believe it should be included as requested.
If you are really worried about someone messing up the data on the drive,
should we not eliminate all write commands?
Hugh
----- Original Message ----- From: "Gary Laatsch" <[EMAIL PROTECTED]> To: "Curtis Stevens" <[EMAIL PROTECTED]>; "T13 List Server" <[EMAIL PROTECTED]> Sent: Monday, June 23, 2003 3:40 PM Subject: Re: [t13] hmmm.. no comments?
This message is from the T13 list server.good
Curtis,
Dropping HDD's is one of those very unsafe thing to do :-)
My 2 cents on the whole deal is simple. Mark Vallis brought up a verypoint in his example of 2 read requests and the 1 write request in thequeueand than overlapped by a FUA Write request. The current ATAPI-7 specor
indicates that the FUA command shall not be released. Obviously if you do
this, the result is the read data returned is in question (return the oldnew data, the command was recieved before but processed after). Also, theinsure
queued write would request data that should be older then the data just
written with the FUA since the command was actually recieved before. I
think this is really an exception case and should be handled as such.
My opinion is to modify the wording to the queued FUA commands to add
something like "if the queued FUA request overlaps a previously queued
command, that the queue shall be flushed....blah blah blah" or however we
say it in T13 queue-ish. The biggest issue is that in this case, the FUA
needs to release and it slows down because of the clean up needed todata integrity. But I know that you guys will figure it out this week upme
there in SJ. Have fun.
Gary Laatsch [EMAIL PROTECTED]
----- Original Message ----- From: "Curtis Stevens" <[EMAIL PROTECTED]> To: "T13 List Server" <[EMAIL PROTECTED]> Sent: Monday, June 23, 2003 10:20 AM Subject: Re: [t13] hmmm.. no comments?
This message is from the T13 list server.
I really don't think the issue is one of implementation... It looks tounexpectedlike there are some concerns about usage and the possibility ofthingsoutcomes. MS clearly stated that they understood several of theunexpectedoutcomes and still needed the capability. There are many "unsafe"asface...you can do to an HDD, but that has not prevented commands from being implemented.
--------------------------- 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 thelong----- Original Message ----- From: "Eschmann, Michael K" <[EMAIL PROTECTED]> To: "T13 List Server" <[EMAIL PROTECTED]> Sent: Monday, June 23, 2003 8:23 AM Subject: RE: [t13] hmmm.. no comments?
This message is from the T13 list server.
My (humble?) opinion is that FUA is necessary and is not dangerous asas a disk drive properly deals with outstanding requests.
First off a flush is very slow, affecting system benchmark scores bywritesmuch 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.performance. The drive should be required to test all outstanding
FUA allows the OS to flush critical data without adversely affectingdevices(in the queued case) and assure that the writes are ordered to guaranteenodata loss. Lets take a look at a specific scenario:over-write the same sector written by the 256 sector write in the
- 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 mustcomplex,cache. The drive must also assure that the media results in the samedata.I'm sure we could expand this simple case to something much moresomeonebut the basic idea remains: The drive must handle ordering such thatthereis no data loss. I've asked once before, and I'll ask it again:willoffer up a more complex scenario where you believe FUA will break and wecanthen 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 cachemydestroy 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 OSdoanother.data was dependent on did such a "FOOLISH" operation I would find
If T13 continues to move towards making it possible for the HOST tonobodybadthings, then the DEVICE is even worse.
We can all pack our bags and go home and switch to T10, becausestackwill 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 toupfromcommandwrite data from both queued and unqueued write commands. A writefollowed by a flush cache command will likely not move the datamadethewritelast write command to the media until the rest of the data is thewritecache is written. If a write FUA command is used the data from thecacheFUA command will be given priority over the other data in the writeServer"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 Listhmmm..<[EMAIL PROTECTED]>oo.com> cc:
Sent by: Subject: Re: [t13]nocomments?[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 asthetothatthe committee. There were many revisions. The only new FUA commandsmakecache.sense are the queued ones. All others could be followed by flush
--------------------------- 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 ofrememberproposalface... ----- 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 theputcommandsforth by Nita didn't contain the QUEUE FUA or QUEUE FUA EXTandwhymemoryhewas wondering where they were added or how they were proposed. Mywasthis was discussed and added at the June 2002 meetings. That isIwaswondering if anyone else remembered these discussions. Ipossiblewellblowigdiscussing all of this stuff (even Andre's comments about the FUAaway the queue) but for some reason it just wasn't captured veryindrivetheminutes.committee.
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 secretBasically, MS stated that they wanted to force meta data to thewithout blowing the que. This means that although it isoftolosedata, 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 partthetheface...----- 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 ofproposal?).origin of the WRITE DMA QUEUED FUA command (where is thecounts.And why no comments on QUEUED EXT commands with large sector"secret
Is this because all these discussions must take place via thesociety"?
Hale
*** Hale Landis *** www.ata-atapi.com ***
