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Old 12-28-2011, 03:57 AM
linux guy
 
Default Implementing a "sometimes" RAID on a laptop. (eSATA, SSD, RAID 1)

I experienced a complete SSD failure this week on my laptop.

I've ordered a new Dell XPS 17 laptop which has an eSATA port.

Given the nature of the SSD failure I experienced, from now on I wish
to have my laptop running a RAID1 setup via the eSATA port when its
used on my desk. However, when its not used on my desk, I wish it to
function normally without the RAID functionality.

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 ?

Question 2.

Internally, my XPS17 has 2 hard drives. I will probably use an SSD
for the OS and a 750 GB 7200 RPM conventional drive for data.

How does one configure the single external eSATA RAID drive to back up
(mirror) the data for both internal drives ?

Question 3.

The OS drive will be an SSD which is faster than the eSATA RAID drive,
which will probably be a 7200 RPM 2TB+ conventional drive. Will this
limit the speed of the SSD to that of the eSATA drive or is buffering
employed to allow one to be faster than the other ?

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 ?

Thanks !
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Old 12-28-2011, 04:43 AM
suvayu ali
 
Default Implementing a "sometimes" RAID on a laptop. (eSATA, SSD, RAID 1)

On Wed, Dec 28, 2011 at 05:57, linux guy <linuxguy123@gmail.com> wrote:
> Given the nature of the SSD failure I experienced, from now on I wish
> to have my laptop running a RAID1 setup via the eSATA port when its
> used on my desk. * However, when its not used on my desk, I wish it to
> function normally without the RAID functionality.

I have never heard of any "sometimes" RAID setup. I don't think that
is possible. I would say just do incremental backups every night.
There are many tools, rsync being the most commonly used. If you use
LVM, you could also try taking LVM snapshots.

I personally use rsnapshot, a wrapper around rsync, to back up every
night. So far it has saved me countless times.

GL

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Suvayu

Open source is the future. It sets us free.
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Old 12-28-2011, 06:04 AM
linux guy
 
Default Implementing a "sometimes" RAID on a laptop. (eSATA, SSD, RAID 1)

On Tue, Dec 27, 2011 at 10:43 PM, suvayu ali
<fatkasuvayu+linux@gmail.com> wrote:
> I have never heard of any "sometimes" RAID setup. I don't think that
> is possible.

I know... it was a longshot.

I would say just do incremental backups every night.
> There are many tools, rsync being the most commonly used. If you use
> LVM, you could also try taking LVM snapshots.

I think I'll use luckybackup or something similar.

> I personally use rsnapshot, a wrapper around rsync, to back up every
> night. So far it has saved me countless times.

I like the fact these tools allow one to save a number of snapshots so
that if you want to look for something from a month ago, you have a
chance of finding it. And they back up without ballooning the
storage requirements as time goes on, other than when you have more
data on your drive.
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Old 12-28-2011, 06:05 AM
linux guy
 
Default Implementing a "sometimes" RAID on a laptop. (eSATA, SSD, RAID 1)

One thing that luckybackup does is send status emails for each backup
attempt. That would be really handy for me.
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Old 12-28-2011, 06:53 AM
Mattias Hellström
 
Default Implementing a "sometimes" RAID on a laptop. (eSATA, SSD, RAID 1)

On Wed, Dec 28, 2011 at 5:57 AM, linux guy <linuxguy123@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.
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Old 12-28-2011, 10:04 AM
Reindl Harald
 
Default Implementing a "sometimes" RAID on a laptop. (eSATA, SSD, RAID 1)

Am 28.12.2011 05:57, schrieb linux guy:
> How does one set up a "sometimes" RAID?

what should this be?

you have two cases:
* RAID
* no RAID

dinish, this was it
only they idea aving "sometimes" a RAID is very strange to say it polite

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