From mboxrd@z Thu Jan 1 00:00:00 1970 From: Doug Ledford Subject: Re: kernel checksumming performance vs actual raid device performance Date: Tue, 23 Aug 2016 15:26:41 -0400 Message-ID: References: <51443e5b-3eef-c35f-8ee7-ad3e85e4e76c@redhat.com> <5416db5c-2d2b-8cc5-b477-604e8ccf0707@redhat.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="hGSrRq140Xdnp61lrccsc1WFGkqOTTjK2" Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: doug@easyco.com Cc: Matt Garman , Mdadm List-Id: linux-raid.ids This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --hGSrRq140Xdnp61lrccsc1WFGkqOTTjK2 Content-Type: multipart/mixed; boundary="4xJvROmaVxnxtr0Dokn06aR4NDSNLVu61" From: Doug Ledford To: doug@easyco.com Cc: Matt Garman , Mdadm Message-ID: Subject: Re: kernel checksumming performance vs actual raid device performance References: <51443e5b-3eef-c35f-8ee7-ad3e85e4e76c@redhat.com> <5416db5c-2d2b-8cc5-b477-604e8ccf0707@redhat.com> In-Reply-To: --4xJvROmaVxnxtr0Dokn06aR4NDSNLVu61 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 8/23/2016 3:19 PM, Doug Dumitru wrote: > Mr. Ledford, >=20 > I am glad that we are in agreement. My issue is that if the customer > is reading 4GB/sec with a non-degraded array, the degraded array > should only have 2X the number of IOs and 2X the transfer sizes to the > drives. If the data rate falls to 1GB, I can suspect cpu overhead. > With this case falling to 200MB/sec, then something else is going on. >=20 > SSDs tend to be very "flat" reading from q=3D1 up to about q=3D20 assum= ing > the HBAs can keep up. Is he using SSDs? If so, I missed that bit. I wrote my response assuming rotating media. --=20 Doug Ledford GPG Key ID: 0E572FDD --4xJvROmaVxnxtr0Dokn06aR4NDSNLVu61-- --hGSrRq140Xdnp61lrccsc1WFGkqOTTjK2 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQIcBAEBCAAGBQJXvKNxAAoJELgmozMOVy/dInAP/2s+6/ZPudJZOHD65qsO3LAE aAk3Sqa5+OoGj/JAl6wBPqPzIT7xrFkRwQB9rLgyv69R3elsxWp181CmeKT7tdAN +0zxTAJt90+g4YNblU3lbJmm/DkUHnRBl18axKZeGWxiCQrn0R5pmKrEx5TFURpu CasaOvQevTGbF9gYWKU0jKU17pGTMr26d6GxE/+w9FcxqcNq+xdEQyFCOYBt7w9i AR8RvT81DUiaXOFSEoqYN8jNXvrpMIxDl97u/466eZEJf03uvHWRa7BGcSdchoYG AZsItK1Agu0SnnRHXBhMqgIPQfLfc9QDKZX3BNZS+hiZac3pPGWmY5weqFO2yPLp VfQNIR3RVhtiDQT/5jB7dv+75czF0Ap1E7HFKshSQAgXSYcFz5AlUDZ/mivur23a Ju0maRWrZTzGazcPKA9+nkMXqwFfeRdV9tcM37py46B7RbX47AwqXQhvVl9bVb9W UL+G3bjQPozHGZ1rvJoPTJZaXQ8+rrvS2Cyb47V0VGPDW9L69wAQ9VMuschCL+qi Tt2gQ+bIWoV+x2eKSNsLHVEoR/a2gRk4DvwONnx4vEgZru3TtdtaztYS+M8h9VAw uMFZp1KmvsZfbb01y53P4zpi9zKBrdAwDdJepeU882Mqo1tpa4CJqTxshzLoq3tY qghW7kl7O2A+f3Pq7BDe =UNBA -----END PGP SIGNATURE----- --hGSrRq140Xdnp61lrccsc1WFGkqOTTjK2--