Date: Mon, 15 Feb 2016 21:08:43 +0000 From: Steven Hartland <killing@multiplay.co.uk> To: freebsd-fs@freebsd.org Subject: Re: Hours of tiny transfers at the end of a ZFS resilver? Message-ID: <56C23E5B.7060207@multiplay.co.uk> In-Reply-To: <8E04E52A-2635-4253-8140-F69495D7D0A6@panasas.com>
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On 15/02/2016 20:33, Ravi Pokala wrote: >> Date: Mon, 15 Feb 2016 21:18:59 +1100 >> From: Andrew Reilly <areilly@bigpond.net.au> >> To: freebsd-fs@freebsd.org >> Subject: Hours of tiny transfers at the end of a ZFS resilver? >> Message-ID: <120226C8-3003-4334-9F5F-882CCB0D28C5@bigpond.net.au> >> Content-Type: text/plain; charset=us-ascii >> >> Hi Filesystem experts, > Hi Andrew, > > I am in no way, shape, or form a filesystem expert. :-) I *am*, however, an ATA drive expert. I wanted to clarify something you said, because it seems to be a common misunderstanding. > >> ... the new drives actually have 4096B sectors (although they lie about that in smartctl -i queries): > They're not lying. > >> Sector Sizes: 512 bytes logical, 4096 bytes physical > Right there - "Sector Size: ... 4096 bytes physical". This is 512B logical / 4KB physical scheme is called AF-512e, and is a documented, standard format. > > https://en.wikipedia.org/wiki/Advanced_Format#512e > > The intent is to allow backwards-compatibility with software going back decades, which only knows about 512-byte sectors. Such software would treat an AF-512e drive the same as any other drive. The trade-off is performance, because the drive has to transparently perform read-modify-write operations (for sub-4096B writes), and read the full 4096B physical sector even if only a single 512B logical sector was requested. (Ditto if a properly-sized but un-aligned request were made.) > > I know GEOM reports both the logical and physical sector sizes (as the provider's "sectorsize" and "stripesize", respectively), and I know that the ATACAM driver is populating them correctly based on the drive's IDENTIFY_DEVICE information. (My very first submission to the project was to fix some bugs in this code; r262886, 2014-03-07.) [*] > > I *don't* know if ZFS does the right thing automatically; it might not be able to determine what "the right thing" is in all cases. I leave answering that to the actual ZFS experts. :-) Yes this was added nearly 2 1/2 years ago by r254591 > > -Ravi (rpokala@) > > [*] This is probably a good segue into discussing why we even have the ADA_Q_4K quirk, and whether we should get rid of it...? --rp The 4k quirks exists because a large amount of devices don't report 4k correctly instead just reporting 512 for both logical and physical even when they are actually 4k or larger physical sector size. Regards Stevehome | help
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