Date: Fri, 31 Jan 2003 18:18:06 +0100 From: phk@freebsd.org To: Steve Byan <stephen_byan@maxtor.com> Cc: freebsd-fs@freebsd.org, tech-kern@netbsd.org Subject: Re: DEV_B_SIZE Message-ID: <2903.1044033486@critter.freebsd.dk> In-Reply-To: Your message of "Fri, 31 Jan 2003 12:03:44 EST." <F4D99E08-353D-11D7-B26B-00306548867E@maxtor.com>
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In message <F4D99E08-353D-11D7-B26B-00306548867E@maxtor.com>, Steve Byan writes : > >On Friday, January 31, 2003, at 11:50 AM, phk@freebsd.org wrote: > >> In message <4912E0FE-3539-11D7-B26B-00306548867E@maxtor.com>, Steve >> Byan writes >> : >> >>> I'd appreciate hearing examples where hiding the underlying physical >>> block size would break a file system, database, transaction processing >>> monitor, or whatever. Please let me know if I may forward your reply >>> to the committee. Thanks. >> >> If by "hide" you mean that there will be no way to discover the >> smallest atomic unit of writes, then you are right: it would be bad. > >The notion is that such a disk would be instantly-compatible with >existing software, modulo performance issues. I suspect this is not the >case, and am searching for expert opinions in this matter. I'm fine with that, as long as the disk somewhere in a data field we can query (if need be with a new request) exposes the smallest atomically writable unit. The only thing that exposes us to risk is we don't know the risk exists, so as long as the fact that a 4k physical sector size is used is not hidden from us, we can adapt. >Yes, I understand recompiling the world for 4K is possible. My question >is whether not doing so poses a data-integrity / fail-recovery risk. Nope. >> It was my impression that already many drives write entire tracks >> as atomic units, at least we have had plenty of anecdotal evidence >> to this effect ? > >I'm not aware of any SCSI or ATA disks which do this; certainly no >Maxtor disk does. Ok, that is nice to know. And yes, we've had our trouble with write caches. Poul-Henning -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message
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