-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Peter, please make sure to use your mail client's reply-to-all feature and avoid any BS reply-to-list command, which breaks cross posted threads, and delays my seeing your reply since I didn't get a copy. On 12/30/2013 6:38 PM, Peter Grandi wrote: > Therefore a larger chunk size increases the amount of data that can > be fetched on each device without waiting for the other device to > get to the desires angular position. It has of course the advnatage > that you mention, but also the advantage that random IO might be > improved. Yes, and that is a good reason not to use 4k chunk size. I believe that 64k is plenty large enough for this purpose though. >> and in the case of raid5 you run into problems with the stripe >> cache. > > IIRC the stripe cache can be up to 32MB for RAID device, and that's > a lot of stripes for any sensible-sized RAID set. But it never > stopped people who "know better" to do very wide RAID5 or RAID6 > sets :-). That's kind of my point: you don't want a *very* large stripe cache, but limiting the chunk size means you get seek overhead to skip the redundant data, so you are stuck between a rock and a hard place. It isn't as big of a deal on a 5 disk raid5/6 but on a 2 or 3 disk raid10, a 512k chunk size has a hefty seek overhead. -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.17 (MingW32) Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBAgAGBQJSxccxAAoJEI5FoCIzSKrwQU4H/RXeLoFe74YFIKaLIc2gs9CM S/RJ2P6ht5ZDR0uWge1t80PcIt46AG61KDoe4uqKeJ8i9j2pnEo74jP4uy8FpIg+ YgwZ114iAthiuA/vL/pQPbbnjJ5t/cG0TBmAviiGEyjckirc6/JO1kwcy3+dL+Fx gfD4f7Vt7CNAkuJyJiyk87cRxJ8o0v643YFuGMnmCdlWr6GDVm/dDOhgtoepK7Mq 9yKm/VLm1Yr5XdCdogK7K7ZnGHLVMKQG8U2+fC1AgsulNtQoEeZmfU47RcK0LSdE Oxb2w5aQb5AwxI6mukpAFTihbKR1qevpffs5qBNSCuTSgiCExj4KAe6BwcAlu9s= =/GBo -----END PGP SIGNATURE----- -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
