Implementing a "sometimes" RAID on a laptop. (eSATA, SSD, RAID 1)

[Mattias Hellström]

On Wed, Dec 28, 2011 at 5:57 AM, linux guy <linuxguy123 at gmail.com> wrote:
> I experienced a complete SSD failure this week on my laptop.
>
> Question 1.
>
> How does one set up a "sometimes" RAID ?   Or would something like
> rsync be better ?   What happens the first time I plug my laptop into
> the eSATA cable after being away from my desk ?  What happens if there
> is both new data and an error in existing data ?  How does the RAID
> software know the difference ?
>

I do think rsync is the right answer but Raid1 with the eSATA drive as
write mostly
is a sometimes raid. You will need a big bitmap (to keep track of what
is new on the ssd) and I suspect it will steal some
performance of your drive even when disconnected.

Keywords: Bitmap Write-intent Logging, write-mostly

> Question 4.
> Can only a portion of the eSATA RAID drive be allocated to the RAID
> and the rest left to be mounted by the laptop for general access ?

Yes. Partition the drive and set some as filesystem and some as raid.

I will give no recipe because you will need to know exactly how this
works to use it, and also do an educated guess on the viability of
this exotic setup after reading the manual.