A puzzling thing about RAID5: syslogd write the log success but another process can not read the /var/log/messages

A puzzling thing about RAID5: syslogd write the log success but another process can not read the /var/log/messages

[Gewj]

hammm,tonight is funny because I got a puzzling thing just as....

my setup is a two-scsi-disk raid5 configuration...
(Linux version 2.4.18-18.7.xsmp (Red Hat Linux 7.3 2.96-112)) #1 SMP Wed
Nov 13 19:01:42 EST 2002)
it work well for a long time, but now I found some day early one of the
scsi disks failed, and I found out
that that time syslogd restarted(why??) and it could write log infor to
log file successfully.
but at the same time , another process(named such as B,run by root) can
not read
the /var/log/messages,or what's more exactly, the messages file was look
like empty to B then.
(of course, the syslogd write log infor to /var/log/messages )

I wonder that if syslogd write the log infor to the well-work scsi disk
, but the process B
read the /var/log/messages from the crashed scsi disk,which cause it
just like a empty file.

yes, it is quite unbelievable. but can some one show me a clue to this
puzzling problem?
What is the proper course of this action?

Re: A puzzling thing about RAID5: syslogd write the log success but another process can not read the /var/log/messages

[Lars Marowsky-Bree]

On 2004-04-07T21:24:01,
   Gewj <geweijin@sinosoft.com.cn> said:

> hammm,tonight is funny because I got a puzzling thing just as....
> 
> my setup is a two-scsi-disk raid5 configuration...

Impossible. RAID5 requires at least three disks.


Sincerely,
    Lars Marowsky-Brée <lmb@suse.de>

-- 
High Availability & Clustering	      \ ever tried. ever failed. no matter.
SUSE Labs			      | try again. fail again. fail better.
Research & Development, SUSE LINUX AG \ 	-- Samuel Beckett

Re: A puzzling thing about RAID5: syslogd write the log success but another process can not read the /var/log/messages

[Neil Brown]

On Wednesday April 7, lmb@suse.de wrote:
> On 2004-04-07T21:24:01,
>    Gewj <geweijin@sinosoft.com.cn> said:
> 
> > hammm,tonight is funny because I got a puzzling thing just as....
> > 
> > my setup is a two-scsi-disk raid5 configuration...
> 
> Impossible. RAID5 requires at least three disks.

Wrong.  RAID5 works fine with just two drives.  Try it.

NeilBrown

(I admit that there isn't a lot of point doing raid5 with two drives
as raid1 should provide identical functionality with better
performance, but it makes an interesting base-line for performances
tests on N-drive arrays).

Re: A puzzling thing about RAID5: syslogd write the log success but another process can not read the /var/log/messages

[Gewj]

thank for your comments

I should say that this question maybe end up without any reasonable result,
the system is now work well , I have give up investigating this problem 
any more.
maybe the question is just cause by the RAID card crash.

Neil Brown wrote:

>On Wednesday April 7, lmb@suse.de wrote:
>  
>
>>On 2004-04-07T21:24:01,
>>   Gewj <geweijin@sinosoft.com.cn> said:
>>
>>    
>>
>>>hammm,tonight is funny because I got a puzzling thing just as....
>>>
>>>my setup is a two-scsi-disk raid5 configuration...
>>>      
>>>
>>Impossible. RAID5 requires at least three disks.
>>    
>>
>
>Wrong.  RAID5 works fine with just two drives.  Try it.
>
>NeilBrown
>
>(I admit that there isn't a lot of point doing raid5 with two drives
>as raid1 should provide identical functionality with better
>performance, but it makes an interesting base-line for performances
>tests on N-drive arrays).
>
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