From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: Re: read-ahead for md/lvm combination Date: Sun, 13 May 2012 07:32:40 +1000 Message-ID: <20120513073240.2d292ec4@notabene.brown> References: <4FAD2866.8070209@pocock.com.au> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=PGP-SHA1; boundary="Sig_/SvxDonyfJtpSNwc2xFe7WMg"; protocol="application/pgp-signature" Return-path: In-Reply-To: <4FAD2866.8070209@pocock.com.au> Sender: linux-raid-owner@vger.kernel.org To: Daniel Pocock Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids --Sig_/SvxDonyfJtpSNwc2xFe7WMg Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Fri, 11 May 2012 14:55:34 +0000 Daniel Pocock wro= te: >=20 >=20 > While I was adding the SCTERC settings to my rc.local, I had a look over > /sbin/blockdev --setra ... settings >=20 > I do things like this, for example: >=20 > /sbin/blockdev --setra 8192 /dev/mapper/myvg-large_media_files >=20 > What about > - the devices /dev/sd[ab]2 > - the md device, /dev/md2 (which is the PV for LVM) ? >=20 > Would it be correct to leave /dev/sd[ab]2 and /dev/md2 at defaults, and > only specify larger sizes for LVs that need it? Or should I even make > /dev/sd[ab]2 and /dev/md2 smaller than the default value (256)? The read-ahead setting is interpreted by the pagecache. So it only makes sense to set in on a device which is directly mounted or accessed via /dev/XXX. On other devices - such as the media device beneath and md array - you can set the read-ahead to anything or nothing and it will have no effect at all. NeilBrown >=20 >=20 > Those disks are SATA - but I'm also planning to add in some SSDs and > RAID1 them with md - they will hold things like source code and home > directories (to make compiling and NFS home directories faster). Can > anyone comment on the read ahead config or any other aspect of such a pla= n? > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html --Sig_/SvxDonyfJtpSNwc2xFe7WMg Content-Type: application/pgp-signature; name=signature.asc Content-Disposition: attachment; filename=signature.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.18 (GNU/Linux) iQIVAwUBT67W+Dnsnt1WYoG5AQJxSg//cFPhbmSBP6ZX12z1+qVHFSzujHdTgXD3 xKBvz8MwtbynU55ofMtDa254g/qq2EdzvfqUmPB3QRQf6XnJ54Bh+eZ3pKywMTgZ gSOL2osZRP40E4bxVYkFNlACzzoLveNxzDqJpnkbCJl6S4crs1ilXEu/ZcF6JsEW vXHUpGTtBRa15WaK7v85AD2wQflRLbl6gDwY1sJzOLwe1r4yhdqsevZ+b7p5baUJ mzykBMBsT1xcWSWnFzCxe0Tsc4s80vUOoegmPtXEXXiVHPd1YIQijepmcmR5vm+9 Vdjdr87pPuqIyTe0tDDqbqT0P8lF9/yeNUnE9Yb0ySv8dlbp9tSJqsp43OKrPuHS 4i5QslE4+g4hAyY6jVOzSthFf8vPYP3JzrQ6R6PzDgnbeiBocBIavXIHrcDvISYB g9dIDvW+7NA3oo0L1gStbUD92ffKd5vIdsM+PUTxKHxX7BHAuS9Agjesn3OkwTlf 4wfpR8n0jT2f6RObw+wPWpPVAHhrM9IHrSg/HIqda1Kgyle6cG+O4rUyLlB2hHFN cWRuLhGqkgrzbXpgnrsjo/b0a22trvSJJuAzfLJo+662XReMig8pqavTrHu5fpvI Olk/mty/PSvm3PKeshaYp+InF+1dODGfXeU1bbo+UiFvw99vTKC79Qweh6lXtdJ8 68hK4ULTuQk= =p+fz -----END PGP SIGNATURE----- --Sig_/SvxDonyfJtpSNwc2xFe7WMg--