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Date: Tue, 20 Oct 2009 16:16:47 -0500 From: Eric Sandeen <sandeen@...hat.com> To: Andreas Dilger <adilger@....com> CC: Doug Hunley <doug@...ley.homeip.net>, linux-ext4@...r.kernel.org Subject: Re: changing stride and stripe_width post-fs-creation? Andreas Dilger wrote: > On 20-Oct-09, at 11:32, Doug Hunley wrote: >> Is it safe to use tune2fs to alter stride and stripe_width on an ext4 >> fs once it has been created? Any caveats I should know about? Thanks > > > The stride is mostly used at fs creation time, but there is no problem > with changing it. The stripe_width is used by the allocator to align > file allocations with the RAID layout. > > One question for Eric is whether the new libdisk patches he made will set > the stripe_width to something ridiculous like 512 or 4096 bytes, or if it > just leaves that field unset in that case. I suspect it would be bad for > mballoc to see the stripe_width be such a small value. well... yes, it does set it to whatever is reported: + min_io = blkid_topology_get_minimum_io_size(tp); + opt_io = blkid_topology_get_optimal_io_size(tp); + blocksize = EXT2_BLOCK_SIZE(fs_param); + + fs_param->s_raid_stride = min_io / blocksize; + fs_param->s_raid_stripe_width = opt_io / blocksize; if mballoc can't handle certain values then maybe the kernel code should be changed to ignore it? Small values could just as easily come from a user too ... -Eric -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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