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Re: How to track down abysmal performance ata - raid1 - crypto - vg/lv -

To: xfs@xxxxxxxxxxx
Subject: Re: How to track down abysmal performance ata - raid1 - crypto - vg/lv - xfs
From: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Date: Thu, 05 Aug 2010 03:33:17 -0500
In-reply-to: <20100805082438.0b476adb@notabene>
References: <20100804073546.GA7494@xxxxxxxxxxxxxxxxxxxxxxxxxx> <20100804085039.GA11671@xxxxxxxxxxxxx> <20100804091317.GA27779@xxxxxxxxxxxxxxxxxx> <20100804092122.GA2998@xxxxxxxxxxxxx> <20100804073546.GA7494@xxxxxxxxxxxxxxxxxxxxxxxxxx> <201008041116.09822@xxxxxx> <20100804102526.GB13766@xxxxxxxxxxxxxxxxxx> <20100804111803.GA32643@xxxxxxxxxxxxx> <alpine.DEB.1.10.1008041351100.19930@xxxxxxxxxxxxxxxx> <20100805082438.0b476adb@notabene>
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Neil Brown put forth on 8/4/2010 5:24 PM:

> Both page-cache and read-ahead work at the filesystem level

Are you referring to /sys/block/sdx/queue/read_ahead_kb?  I'm pretty sure this
works below the FS level and below the partition level.  This read_ahead works
at the block device level.  At least for individual or JBOD.

Are you saying this setting gets ignored by the kernel if/when mdadm, LVM,
and/or crypto are used?

-- 
Stan

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