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Date: Fri, 22 Nov 2013 20:57:16 +0100 From: Stefan Priebe <s.priebe@...fihost.ag> To: "J. Bruce Fields" <bfields@...ldses.org>, Theodore Ts'o <tytso@....edu>, Chinmay V S <cvs268@...il.com>, Christoph Hellwig <hch@...radead.org>, linux-fsdevel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>, LKML <linux-kernel@...r.kernel.org>, matthew@....cx Subject: Re: Why is O_DSYNC on linux so slow / what's wrong with my SSD? Am 20.11.2013 16:55, schrieb J. Bruce Fields: > On Wed, Nov 20, 2013 at 10:37:03AM -0500, Theodore Ts'o wrote: >> On Wed, Nov 20, 2013 at 08:52:36PM +0530, Chinmay V S wrote: >>> >>> If you have confirmed the performance numbers, then it indicates that >>> the Intel 530 controller is more advanced and makes better use of the >>> internal disk-cache to achieve better performance (as compared to the >>> Intel 520). Thus forcing CMD_FLUSH on each IOP (negating the benefits >>> of the disk write-cache and not allowing any advanced disk controller >>> optimisations) has a more pronouced effect of degrading the >>> performance on Intel 530 SSDs. (Someone with some actual info on Intel >>> SSDs kindly confirm this.) >> >> You might also want to do some power fail testing to make sure that >> the SSD is actually flusing all of its internal Flash Translation >> Layer (FTL) metadata to stable storage on every CMD_FLUSH command. > > Some SSD's are also claim the ability to flush the cache on power loss: > > http://www.intel.com/content/www/us/en/solid-state-drives/ssd-320-series-power-loss-data-protection-brief.html > > Which should in theory let them respond immediately to flush requests, > right? Except they only seem to advertise it as a safety (rather than a > performance) feature, so I probably misunderstand something. Yes but they all should make use and support CMD_FLUSH so it's slow on them too. > And the 520 doesn't claim this feature (look for "enhanced power loss > protection" at http://ark.intel.com/products/66248), so that wouldn't > explain these results anyway. Correct i think intel simply ignores CMD_FLUSH on that drive - no idea why an they fixed this for their 330, 530, DC S3500 (all tested) > --b. > >> >> There are lots of flash media that don't do this, with the result that >> I get lots of users whining at me when their file system stored on an >> SD card has massive corruption after a power fail event. >> >> Historically, Intel has been really good about avoiding this, but >> since they've moved to using 3rd party flash controllers, I now advise >> everyone who plans to use any flash storage, regardless of the >> manufacturer, to do their own explicit power fail testing (hitting the >> reset button is not good enough, you need to kick the power plug out >> of the wall, or better yet, use a network controlled power switch you >> so you can repeat the power fail test dozens or hundreds of times for >> your qualification run) before being using flash storage in a mission >> critical situation where you care about data integrity after a power >> fail event. >> >> IOW, make sure that the SSD isn't faster because it's playing fast and >> loose with the FTL metadata.... >> >> Cheers, >> >> - Ted >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in >> the body of a message to majordomo@...r.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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