Date: Thu, 23 Oct 2003 12:46:26 -0700 From: Kirk McKusick <mckusick@beastie.mckusick.com> To: Ken Marx <kmarx@vicor.com> Cc: Julian Elischer <julian@vicor.com> Subject: Re: 4.8 ffs_dirpref problem Message-ID: <200310231946.h9NJkQeN007683@beastie.mckusick.com> In-Reply-To: Your message of "Thu, 23 Oct 2003 11:08:02 PDT." <3F981902.90607@vicor.com>
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Date: Thu, 23 Oct 2003 11:08:02 -0700 From: Ken Marx <kmarx@vicor.com> To: Julian Elischer <julian@vicor.com> CC: mckusick@mckusick.com, cburrell@vicor.com, davep@vicor.com, freebsd-fs@freebsd.org, gluk@ptci.ru, jpl@vicor.com, jrh@vicor.com, julian@vicor-nb.com, VicPE@aol.com Subject: Re: 4.8 ffs_dirpref problem X-ASK-Info: Confirmed by User Thanks for the reply, We actually *did* try -s 4096 yesterday (not quite what you suggested) with spotty results: Sometimes it seemed to go more quickly, but often not. Let me clarify our test: We have a 1.5gb tar file from our production raid that fairly represents the distribution of data. We hit the performance problem when we get to dirs with lots of small-ish files. But, as Julian mentioned, we typically have many flavors of file sizes and populations. Admittedly, our untar'ing test isn't necessarily representitive of what happens in production - we were just trying to fill the disk and recreate the problem here. We *did* at least hit a noticeable problem, and we believe it's the same behavior that's hitting production. I just tried your exact suggested settings on an fs that was already 96% full, and still experienced the very sluggish behavior on exactly the same type of files/dirs. Our untar typically takes around 60-100 sec of system time when things are going ok; 300-1000+ sec when the sluggishness occurs. This time tends to increase as we get closer to 99%. Sometimes as high as 4000+ secs. I wasn't clear from your mail if I should newfs the entire fs and start over, or if I could have expected the settings to make a difference for any NEW data. I can do this latter if you think it's required. The test will then take several hours to run since we need at least 85% disk usage to start seeing the problem. Thanks! k Unfortunately, I do believe that you will need to start over from scratch with a newfs. The problem is that by the time you are at 85% full with the old parameters, the directory structure is already too "dense" forcing you to search far and wide for more inodes. If you start from the beginning with a large filesperdir then your directory structure will expand across more of the disk which should approximate the old algorithm. Kirk McKusick
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