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Re: Delaylog

To: xfs@xxxxxxxxxxx
Subject: Re: Delaylog
From: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Date: Tue, 14 Sep 2010 15:03:24 -0500
In-reply-to: <201009142106.24448.arekm@xxxxxxxx>
References: <AANLkTin6FSBK3tMXhSxDuLdjyb+R0LhNnaa2CKt37FcV@xxxxxxxxxxxxxx> <201009142106.24448.arekm@xxxxxxxx>
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.9.2.9) Gecko/20100825 Thunderbird/3.1.3
Arkadiusz Miskiewicz put forth on 9/14/2010 2:06 PM:
> On Tuesday 14 of September 2010, Fabricio Archanjo wrote:
>> Hey all,
>>
>>    I just trying delaylog in my server that has a mysql database. When
>> i monted my /var/lib/mysql with delaylog option, it showed me:
>> "Enabling EXPERIMENTAL delayed logging feature - use at your own
>> risk". Ok, i know it's experimental, but what kind of problem could i
>> have using delaylog?
> 
> ... and what problems in case of system hang or power loss when compared to 
> nodelaylog mode?

This was covered in prior posts IIRC.  Delaylog holds more write
transactions in memory in an effort to decrease the amount of disk I/O
and optimize write patterns.  The more blocks waiting in the in memory
log, the more data will be lost due to power outage, controller/disk
failure, storage HBA/network failure (iSCSI/FC), kernel panics, etc.

Same failure modes as before, but with potentially greater loss of
data--unless there is an undiscovered bug that can wreck the entire
filesystem.  ;)  Which I believe is the reason for the "experimental"
boilerplate.

-- 
Stan

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