linux-ext4 - Re: [RFC] store RAID stride in superblock

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Message-ID: <20070524114442.GA12526@schatzie.adilger.int>
Date:	Thu, 24 May 2007 05:44:42 -0600
From:	Andreas Dilger <adilger@...sterfs.com>
To:	linux-ext4@...r.kernel.org
Cc:	Theodore Ts'o <tytso@....edu>
Subject: Re: [RFC] store RAID stride in superblock

On May 22, 2007  01:22 +0530, Kalpak Shah wrote:
>         __u16   s_raid_stride;          /* RAID stride */
> -       __u16   s_pad;                  /* Padding */
> +       __u16   s_mmp_interval;         /* Wait for # seconds in MMP
> checking */
> +       __u64   s_mmp_block;            /* Block for multi-mount protection
> */

Ted, I just noticed this updated patch w.r.t. your recent s_raid_stride
addition.  I also want to have a separate parameter for "s_raid_stripe_width"
which is normally N * s_raid_stride, where N is the number of disks in a
RAID 5 N+1 (or RAID 6 N+2) parity stripe.  This is for delalloc+mballoc to
allow it to align and size new allocations so that writes do not impose
read-modify-write overhead on the RAID stripes.

My understanding from the code is that s_raid_stride is to put the bitmaps
for different groups on different disks to avoid always having a single
disk busy with bitmap updates.

Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.

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