[CentOS] RAID help

Tue Dec 14 23:14:10 UTC 2010
Markus Falb <markus.falb at fasel.at>

On 14.12.2010 23:27, Les Mikesell wrote:
> On 12/14/2010 4:16 PM, Markus Falb wrote:
>> On 14.12.2010 22:49, Jason T. Slack-Moehrle wrote:
>>> Hi,
>>>
>>>> If you dont know in advance how your storage is allocated the best way,
>>>> use lvm. The space you dont need today is in the pool and be it
>>>> /var/www/html or swap or whatever assign it as needed in the future.
>>>>
>>>> Note that its maybe better to not put /boot into lvm.
>>>>
>>>> I would suggest
>>>>
>>>> /dev/md0 ->  /boot
>>>> /dev/md1 ->  lvm with all other partitions including swap
>>>
>>> OK, I have done this, I need to create mount points and I am not sure how to initially size.
>>
>> My idea was to assign minimum at now. It could go like this:
>>
>> lvm volume group ->  1000GB
>>
>> for the system:
>> lvm logical volume for / ->  1GB
>> lvm logical volume for /var ->  1GB
>> lvm logical volume for /usr ->  1GB
>>
>> lvm logical volume for /var/www/html ->  50GB
>>
>> Now you have assigned 53GB out of the 1000 and the other 947GB remains
>> dynamically assignable from the lvm volume group.
>>
>> If you need more space in one of the partitions, just grow it, out of
>> the pool of 947GB. Logical Volumes can be resized online and many
>> filesystems can be grown online (mounted) too. If the initial 1GB for
>> some partition proves to be to low, e.g. it has to be increased on every
>> server you have than adjust it to initial 2GB or whatever size is
>> adequat for you. I am not after numbers at all. My point is: If you dont
>> know how to partition, assign at minimum, allowing for future flexibility.
> 
> But this only helps if you don't know where you will need to grow.  If 
> you know it is going to be under /var, just give it all the space you 
> have in the first place and avoid the overhead of lvm.

To quote Jason, the OP: "what should my SWAP space be" ?
How should I know ? lvm to the rescue.

lvm also helps if you want to have additional partitions. Maybe one day
you recognise that a separate partition for /var/log/httpd would be a
good thing.

You are talking about the performance overhead ? Not sure about that. I
think the flexibility you gain makes it at least worth thinking about
it. Said that, I would be interested in hearing about disadvantages of lvm.

-- 
Best Regards,
Markus Falb

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