From owner-freebsd-fs Fri Jan 31 10:56: 9 2003 Delivered-To: freebsd-fs@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 86A7237B401 for ; Fri, 31 Jan 2003 10:56:06 -0800 (PST) Received: from apollo.email.starband.net (smtp2.starband.net [148.78.247.23]) by mx1.FreeBSD.org (Postfix) with ESMTP id 81A8943F75 for ; Fri, 31 Jan 2003 10:56:05 -0800 (PST) (envelope-from jkirby@storagecraft.com) Received: from jkirbydesk (vsat-148-63-114-177.c002.t7.mrt.starband.net [148.63.114.177]) (authenticated bits=0) by apollo.email.starband.net (8.12.4/8.12.4) with ESMTP id h0VItoH5024439; Fri, 31 Jan 2003 13:55:55 -0500 Reply-To: From: "Jamey Kirby" To: "'Steve Byan'" , "'David Laight'" Cc: , Subject: RE: DEV_B_SIZE Date: Fri, 31 Jan 2003 10:55:47 -0800 Organization: StorageCraft Message-ID: <001601c2c95a$63d52d70$0300a8c0@jkirbydesk> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.4024 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Importance: Normal In-Reply-To: <1BBFD4B2-354C-11D7-B26B-00306548867E@maxtor.com> Sender: owner-freebsd-fs@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.org I have been a lurker for years and want to chime in. Under Windows NT (all flavors), using a 4K sector size works fine. The OS abstraction layers are very good and handling the alignment. I wrote a virtual SCSI disk driver (ATA is presented as SCSI to the NT OS kernel) and experimented with all sorts of sector sizes to see how various software would handle it. I found no problems... However, I myself have written test code in the past that assumes 512 byte sectors rather than reading the sector size from the OS. Surly this code would break. Jamey Kirby StorageCraft -----Original Message----- From: owner-freebsd-fs@FreeBSD.ORG [mailto:owner-freebsd-fs@FreeBSD.ORG] On Behalf Of Steve Byan Sent: Friday, January 31, 2003 10:45 AM To: David Laight Cc: freebsd-fs@FreeBSD.ORG; tech-kern@netbsd.org Subject: Re: DEV_B_SIZE On Friday, January 31, 2003, at 12:59 PM, David Laight wrote: > On Fri, Jan 31, 2003 at 11:30:18AM -0500, Steve Byan wrote: >> There's a notion afoot in IDEMA to enlarge the underlying physical >> block size of disks to 4096 bytes while keeping a 512-byte logical >> block size for the interface. Unaligned accesses would involve either >> a >> read-modify-write or some proprietary mechanism that provides >> persistence without the latency cost of a read-modify-write. > > There probably ought to be a way of making the larger physical > size visible to systems that are willing to support larger > block sizes. That way misaligned transfers would be far less > likely. Yes, of course. But I asked with respect to an issue other than performance. > > One problem to consider is that disks are still partitioned > on cylinder boundaries. This is largely historic but isn't > this doen't actually make much sense, since the geometry > almost certainly varies across the disk and has to be faked > to fit the ATA CHS limits and (on PCs) the BIOS interface. > > However what it does mean is that a partition could easily > not start on a 8 (512 byte) sector boundary. > So misaligned transefers are likely even if the filesystem > itself is using 4k blocks. > > On a PC the partitioning will typically have the first one > starting in sector 63, and the others at multiple of 16065 > sectors from the start of the disk). > > This doesn't bode well for getting any aligned transfer > at all. We understand that problem. It's just a performance issue. My concern is that even if we handwave the performance issues, there's an underlying semantic that would not be satisfied if we were to run existing software, unmodified, on a disk with an underlying 4K sector size. Regards, -Steve -------- Steve Byan Design Engineer Maxtor Corp. MS 1-3/E23 333 South Street Shrewsbury, MA 01545 (508) 770-3414 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message