From mboxrd@z Thu Jan 1 00:00:00 1970 From: Roman Mamedov Subject: Re: Optimal value for bitmap-chunk option Date: Wed, 19 Jun 2013 10:38:38 +0600 Message-ID: <20130619103838.7c3fb6e0@natsu> References: <51C057F9.3020005@qwarta.ru> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=PGP-SHA1; boundary="Sig_//ojbf6g84OJnvb4sC6wRLSJ"; protocol="application/pgp-signature" Return-path: In-Reply-To: <51C057F9.3020005@qwarta.ru> Sender: linux-raid-owner@vger.kernel.org To: =?UTF-8?B?0KDQvtC80LDQvSDQkNC70LXQutGB0LXQtdCy?= Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids --Sig_//ojbf6g84OJnvb4sC6wRLSJ Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Tue, 18 Jun 2013 16:52:09 +0400 =D0=A0=D0=BE=D0=BC=D0=B0=D0=BD =D0=90=D0=BB=D0=B5=D0=BA=D1=81=D0=B5=D0=B5= =D0=B2 wrote: > Hello, >=20 > I want to speed up rebuilding process of the raid to do that I'm going > to apply the command: >=20 > mdadm --grow --bitmap=3Dinternal --bitmap-chunk=3DNNNN /dev/mdX >=20 > But I don't know how to calculate optimal value of bitmap-chunk option. > How can I do that? It's just the minimum granularity of pieces that get rebuilt after unclean shutdowns. E.g. if your array decides it's "dirty" in 5 different areas, wi= th a 16MB chunk the rebuild will process 5*16MB, but with a 128MB it will rebu= ild 5*128MB. On modern systems the difference in time required to do the rebuild between these two will be negligible. But having a larger size helps noticeably in everyday operation (makes writes faster). So there is nothing= to "calculate" really, just use a reasonably large size like 128 or 256 MB. https://raid.wiki.kernel.org/index.php/Write-intent_bitmap http://techblog.tgharold.com/2013/01/mdadm-using-bitmaps-to-speed-up-rebuil= ds.html http://blog.liw.fi/posts/write-intent-bitmaps/ (the 1st comment) --=20 With respect, Roman --Sig_//ojbf6g84OJnvb4sC6wRLSJ Content-Type: application/pgp-signature; name=signature.asc Content-Disposition: attachment; filename=signature.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iEYEARECAAYFAlHBNc4ACgkQTLKSvz+PZwjKpQCfckXwud7Sbgg5XECZ2hcIltfK KlcAn2xWH4BZNVU10bjjL/MQ7357Mflk =44SF -----END PGP SIGNATURE----- --Sig_//ojbf6g84OJnvb4sC6wRLSJ--