Questions on Partitioning across two drives

Jim mickeyboa at sbcglobal.net
Mon May 11 15:05:04 UTC 2009


Kevin J. Cummings wrote:
> Jim wrote:
>> Kevin J. Cummings wrote:
>>> Jim wrote:
>>>> Patrick W. Barnes wrote:
>>>>> On Sunday 10 May 2009 18:04:35 Jim wrote:
>>>>>  
>>>>>> I have a EeePC 1000 with two SSD drives and Fedora 10.
>>>>>> I want to make /  partition larger
>>>>>> sda1 / 8gb
>>>>>> sdb1 /home 32gb
>>>>>>
>>>>>> I want to make /home 20gb
>>>>>> I want to make /   20gb
>>>>>>
>>>>>> I have  made sdb1 /home 20gb with Gparted and I made with the
>>>>>> unallocated space a   / ext3 primary partition.
>>>>>> how do I make that / partition to join with the /  on  sda1 ?
>>>>>>     
>>>>>
>>>>> You will have to create a software RAID0 device that spans across 
>>>>> both drives and includes all of the space you want used for /, 
>>>>> then create a new partition for / within that RAID device.
>>>>>
>>>>>   
>>>> What Raid Type would I use ?
>>>>
>>>
>>> You have 2 choices:
>>>
>>> 1) Create a RAID-0 partition which spans both drives.  This results 
>>> in a single partition.  The drives need to be the same size in order 
>>> for the striping to work.  These drives are not the same size.  You 
>>> could stripe the first 8GB for a 16 GB partition, but it would leave 
>>> you with a 24 GB 2nd partition on sdb, 16/24 is not quite what you 
>>> want.
>>>
>>> 2) Use LVM to merge the 2 physical partitions into a single logical 
>>> volume which spans both drives.  Since both logical partitions can 
>>> be allocated out of the single logical volume, you can make them 
>>> whatever size you need (ie, both of 20GB should be doable).
>>>
>> I can make both partitions the same .
>> sda1 8gb
>> sdb2  8gb
>> Total 16gb for /
>>
>> And put the remainder in sdb1 /home.
>>
>> I guess I will settle for a Raid 0
>>
>> But how would a  Raid 5 do ?
>
> You don't have enough disks for a real RAID-5.  You need a minumum of 
> 3 "disks".  RAID-5 is designed so that you can be doing a write of 
> data and a write of the "parity" data for each write.  Reads can be 
> done quicker since the more "disks" in your stripe, the better the 
> possibility that 2 concurrent reads will use different disks to access 
> the required data, possibly doing it faster (in parallel instead of 
> serially) and with the possibility of still being able to access your 
> data even if one of your disk drives fails (RAID-6 provides for a 
> possible double failure by adding a 2nd parity disk in the array).
>
> Note:  RAID-0 has no parity data, so no redundancy in case of hardware 
> failure.  But the striping could lead to quicker read or write times 
> since you would have 2 disks to spread the operations over instead of 
> having only one and having to wait for a previous operation to finish 
> before doing a 2nd one.
>
> Your choices with only 2 physical spindles is either RAID-0 (striping) 
> or RAID-1 (mirroring).
>
Thanks Kevin for your help on this.
Can I change a ext3 partition  (sda1) with  data on it to raid 0 or do I 
have to do a fresh install ?




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