From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Anton Mitterer Subject: Re: some general questions on RAID Date: Sun, 07 Jul 2013 20:01:52 +0200 Message-ID: <1373220112.5246.20.camel@fermat.scientia.net> References: <1372962602.8716.56.camel@heisenberg.scientia.net> <51D5F22C.70007@turmel.org> <51D9A7CF.6000700@gmail.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg="sha1"; protocol="application/x-pkcs7-signature"; boundary="=-6jJXpj1WaWOoYVlmq+1O" Return-path: In-Reply-To: <51D9A7CF.6000700@gmail.com> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org Cc: Milan Broz List-Id: linux-raid.ids --=-6jJXpj1WaWOoYVlmq+1O Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hi Milan. Thanks for your answers :) On Sun, 2013-07-07 at 19:39 +0200, Milan Broz wrote: > dmcrypt keeps IO running on the CPU core which submitted it. >=20 > So if you have multiple IOs submitted in parallel from *different* CPUs, > they are processed in parallel. >=20 > If you have MD over dmcrypt, this can cause problem that MD sumbits all I= Os > with the same cpu context and dmcrypt cannot run it in parallel. Interesting to know :) I will ask Arno over at the dm-crypt list to at this to the FAQ. I'd guess there are no further black magical issues one should expect when mixing MD and/or dmcrypt with LVM (especially when contiguous allocation is used)... and even less expectable when using partitions (should be just offsetting)?! > (Please note, this applies for kernel with patch above and later, > previously it was different. There were a lot of discussions about it, > some other patches which were never applied to mainline etc, see dmcrypt > and dm-devel list archive for more info...) IIRC, than these included discussions about paralleling IO sent from one CPU context, right? That's perhaps a bit off-topic now,... but given that stacking dmcrypt with MD seems to be done by many people I guess it's not totally off-topic, so... Are there any plans for that (paralleling IO from one core)? Which should make it (at least performance wise) okay again do but dmcrypt below MD (not that I'd consider that much useful, personally). > Block layer (including transparent mappings like dmcrypt) can > reorder requests. It is FS responsibility to handle ordering (if it is > important) though flush requests. Interesting... but I guess the main filesystems (ext*, xfs, btrfs, jfs) do just right with any combinations of MD/LVM/dmcrypt? Lots of thanks again, Chris. --=-6jJXpj1WaWOoYVlmq+1O Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIIQ/jCCBXUw ggNdoAMCAQICAwEBgjANBgkqhkiG9w0BAQUFADBUMRQwEgYDVQQKEwtDQWNlcnQgSW5jLjEeMBwG A1UECxMVaHR0cDovL3d3dy5DQWNlcnQub3JnMRwwGgYDVQQDExNDQWNlcnQgQ2xhc3MgMyBSb290 MB4XDTEyMDcyMzE0NTY0NVoXDTE0MDcyMzE0NTY0NVowfDEhMB8GA1UEAxMYQ2hyaXN0b3BoIEFu dG9uIE1pdHRlcmVyMSQwIgYJKoZIhvcNAQkBFhVjYWxlc3R5b0BzY2llbnRpYS5uZXQxMTAvBgkq hkiG9w0BCQEWIm1haWxAY2hyaXN0b3BoLmFudG9uLm1pdHRlcmVyLm5hbWUwggEiMA0GCSqGSIb3 DQEBAQUAA4IBDwAwggEKAoIBAQCq/4X3Urm/IHCIYUyqPrBN6FZ2pmd8V5epPyDlveqtdYvLBLNy gP3G3KhGoCA4Jf49KYGmbqk+F7fVWcG1zcdwEx7itKJyj39nYf2HWXogxUSfKFptbOgpsTcEWuxg ka2EkJuErTvYbwCEKT7mn4v6ScuFBc3Q+Hswlt1jbqjczi+OxcU1skvxM5jGjzRwYPUsiHZJRkWp ogbbhNWZNbwXiMPln380TAlryRAr5UE0dSe1dg1qHhF6HSNKwaer0+Dcd/goL4XQhHxCAGZKfCK0 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