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Re: xfs_growfs / planned resize / performance impact

To: Martin Steigerwald <Martin@xxxxxxxxxxxx>
Subject: Re: xfs_growfs / planned resize / performance impact
From: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Date: Sun, 05 Aug 2012 07:34:58 -0500
Cc: xfs@xxxxxxxxxxx, Eric Sandeen <sandeen@xxxxxxxxxxx>, Stefan Priebe - Profihost AG <s.priebe@xxxxxxxxxxxx>
In-reply-to: <201208051303.09337.Martin@xxxxxxxxxxxx>
References: <5017E426.2040709@xxxxxxxxxxxx> <501B4D7E.1000303@xxxxxxxxxxx> <501B6B04.2090002@xxxxxxxxxxxx> (sfid-20120803_140801_426027_0A33D973) <201208051303.09337.Martin@xxxxxxxxxxxx>
Reply-to: stan@xxxxxxxxxxxxxxxxx
User-agent: Mozilla/5.0 (Windows NT 5.1; rv:14.0) Gecko/20120713 Thunderbird/14.0
On 8/5/2012 6:03 AM, Martin Steigerwald wrote:

> Well the default was 16 AGs for volumes < 2 TiB AFAIR. And it has been 
> reduced to 4 for as I remember exactly performance reasons. Too many AGs 
> on a single device can incur too much parallelity. Thats at least is what 
> I have understood back then.

For striped md/RAID or LVM volumes mkfs.xfs will create 16 AGs by
default because it reads the configuration and finds a striped volume.
The theory here is that more AGs offers better performance in the
average case on a striped volume.

With hardware RAID or a single drive, or any storage configuration for
which mkfs.xfs is unable to query the parameters, mkfs.xfs creates 4 AGs
by default.  The 4 AG default has been with us for a very long time.  It
was never reduced.


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