Questions on Partitioning across two drives

[Kevin J. Cummings]

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).

-- 
Kevin J. Cummings
kjchome at rcn.com
cummings at kjchome.homeip.net
cummings at kjc386.framingham.ma.us
Registered Linux User #1232 (http://counter.li.org)