mdadm.conf questions

mdadm.conf questions

[Herta Van den Eynde]

When I run "mdadm --detail --scan", the command outputs information about the devices in the array on a separate line:

# mdadm --detail --scan
ARRAY /dev/md3 level=raid0 num-devices=3 UUID=fc5d996b:15107473:e3e819c9:6829a450
   devices=/dev/md0,/dev/md1,/dev/md2
ARRAY /dev/md2 level=raid1 num-devices=2 UUID=32d034b8:e93cc8c7:f6335e14:829aefee
   devices=/dev/sde,/dev/sdh
ARRAY /dev/md1 level=raid1 num-devices=2 UUID=4efa3017:9dc3fa9b:6f4acac4:e1944bec
   devices=/dev/sdd,/dev/sdg
ARRAY /dev/md0 level=raid1 num-devices=2 UUID=1d078c62:2b90a2c3:1ec1d0af:75600395
   devices=/dev/sdc,/dev/sdf

1. When I redirect this output to '/etc/mdadm.conf, should I then edit the file to join the line listing the devices to the one defining the ARRAY?
2. Should the devices tag be there at all?  sd[c-e] are on a separate bus from sd[f-h].  If I add more devices to the first bus, sd[f-h] will be renamed.  Won't that confuse the md driver? 
3. should I add /dev/md[0-2] as DEVICE in /etc/mdstat.conf?

Kind regards,

Herta

Re: mdadm.conf questions

[Herta Van den Eynde]

Thanks for your prompt reply, Neil.

You're right - of course - about the man pages.  Only, if you're new to 
this, it's not always evident to determine what constitutes "unwanted 
detail".  Thanks for explaining.

Kind regards,

Herta

Neil Brown wrote:

>On Thursday May 15, herta.vandeneynde@cc.kuleuven.ac.be wrote:
>  
>
>>When I run "mdadm --detail --scan", the command outputs information about the devices in the array on a separate line:
>>
>># mdadm --detail --scan
>>ARRAY /dev/md3 level=raid0 num-devices=3 UUID=fc5d996b:15107473:e3e819c9:6829a450
>>   devices=/dev/md0,/dev/md1,/dev/md2
>>ARRAY /dev/md2 level=raid1 num-devices=2 UUID=32d034b8:e93cc8c7:f6335e14:829aefee
>>   devices=/dev/sde,/dev/sdh
>>ARRAY /dev/md1 level=raid1 num-devices=2 UUID=4efa3017:9dc3fa9b:6f4acac4:e1944bec
>>   devices=/dev/sdd,/dev/sdg
>>ARRAY /dev/md0 level=raid1 num-devices=2 UUID=1d078c62:2b90a2c3:1ec1d0af:75600395
>>   devices=/dev/sdc,/dev/sdf
>>
>>1. When I redirect this output to '/etc/mdadm.conf, should I then
>>edit the file to join the line listing the devices to the one
>>defining the ARRAY? 
>>    
>>
>
>Only if you want to.  mdadm is happy with continuing a line in the
>next line if it is indented.
>
>  
>
>>2. Should the devices tag be there at all?  sd[c-e] are on a
>>separate bus from sd[f-h].  If I add more devices to the first bus,
>>sd[f-h] will be renamed.  Won't that confuse the md driver?  
>>    
>>
>
>No, the device tag normally is not needed.  I think the man page makes
>a point of saying that the output of --detail --scan is only the
>starting point of an mdadm.conf.  You need to edit it based on how
>your system is managed.  In some cases, e.g. ide drives, a devices
>entry is a good idea.  In most cases, and particularly with SCSI it
>isn't.
>
>  
>
>>3. should I add /dev/md[0-2] as DEVICE in /etc/mdstat.conf?
>>    
>>
>
>Yes.
>
>NeilBrown
>  
>

4k issue on MD device block size

[bmoon]

Hello,

Please provide me an advice on  the following issues;

I'd like to use 4k block size for both MD super block I/O and regular file
I/O,
which will improve the performance.

Q1: I noticed that it set the "blksize_size" to 4k for MD SB I/O but it use
1K
       for the regular file I/O.  It usually set the size to 1k at system
init by "md-init",
       then it set to 4k for MD SB I/O later. I could not find the place
that set it
      back to 1k.   However, it changes to 1 k????  How?

Q2: I modified md.c to use the 4k blksize_size. It works but sometimes it
crash.
      System "BLOCK_SIZE" is still 1k, and my hd device blksize_size=1k,
too.
      I changed ONLY 1024 to 4096 on every occurences on md.c.

     What am I missing?

Thanks in advance,

Bo