From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ric Wheeler Subject: Re: impact of 4k sector size on the IO & FS stack Date: Mon, 12 Mar 2007 09:32:14 -0400 Message-ID: <45F5565E.7010104@emc.com> References: <45F48809.2060908@emc.com> <20070312000253.20eab1a3@lxorguk.ukuu.org.uk> <45F4A268.3000405@garzik.org> <20070312122424.18ed86ce@lxorguk.ukuu.org.uk> Reply-To: ric@emc.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20070312122424.18ed86ce@lxorguk.ukuu.org.uk> Sender: linux-fsdevel-owner@vger.kernel.org To: Alan Cox Cc: Jeff Garzik , linux-scsi , linux-fsdevel@vger.kernel.org, Linux-ide List-Id: linux-ide@vger.kernel.org Alan Cox wrote: >> First generation of 1K sector drives will continue to use the same >> 512-byte ATA sector size you are familiar with. A single 512-byte write >> will cause the drive to perform a read-modify-write cycle. This >> configuration is physical 1K sector, logical 512b sector. > > The problem case is "read-modify-screwup" > > At that point we've trashed the block we were writing (a well studied > recovery case), and we've blasted some previously sane, totally > unrelated sector of data out of existance. Thats why we need to know > ideally if they are doing the write to a different physical block when > they do this, so that we don't lose the old data. My guess is they won't > as it'll be hard. I think that the firmware would have to do this in the drive's write cache and would always write the modified data back to the same physical sector (unless a media error forces a sector remap). If firmware modifies the 7 512 byte sectors that it read to do the 1 512 byte sector write, then we certainly would see what you describe happen. In general, it would seem to be a bad idea to do allocate a different physical sector to underpin this king of read-modify-write since that would kill contiguous layout of files, etc. >> A future configuration will change the logical ATA interface away from >> 512-byte sectors to 1K or 4K. Here, it is impossible to read a quantity >> smaller than 1K or 4K, whatever the sector size is. > > That one I'm not worried about - other than "guess how Redmond decide to > make partition tables work" that one is mostly easy (be fun to see how > many controllers simply can't cope with the command formats) > This will be interesting to find out. I will be sharing a panel with some BIOS & MS people, so I will update all on what I hear, ric