Upgrading a RAID system

  • Thread starter Thread starter Mao
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M

Mao

Dear all, I'm a newbie on the RAID system. I just read something on
wiki and on other website.
Since my external USB HD is getting full, I wanted to integrate it
with a NAS.
Let's assume I buy a 4 bays NAS with 2 500 GB HD mounted. Then I will
add an old 180 GB HD.
Now the questions:

1) Can I create 2 volumes (if volume is the right word) one 3x180 GB
RAID 5 for 360 GB of space (more or less) and the other 2x320 GB RAID
1/5 for additional 320 GB (Total 680 GB out of 1180)?

2) If later I add a 4th HD, for example a 750 GB HD, can I upgrade the
system without losing data and without doing any external backup to a
2 volumes systems with one 4x180 GB RAID 5 for 540 GB of space and the
other 3x320 GB RAID 5 for additional 640 GB and eventually a volume
single HD of 250 GB (TOTAL 1430 GB out of 1930)

3) If later I substitute the smallest HD with a 750 GB HD, can I
upgrade the system without losing data and without doing any external
backup to a 3 volumes systems with one 4x180 GB RAID 5 for 540 GB of
space, one 4 x320 GB RAID 5 for additional 960 GB and the other 2x250
for additional 250 GB (TOTAL 1750 GB out of 2500)

If yes for all the questions, which NAS on the market allow me to do
this upgrade friendly?

Thanks a lot and sorry for the long message
Bye MAO
 
Previously Mao said:
Dear all, I'm a newbie on the RAID system. I just read something on
wiki and on other website.
Since my external USB HD is getting full, I wanted to integrate it
with a NAS.
Let's assume I buy a 4 bays NAS with 2 500 GB HD mounted. Then I will
add an old 180 GB HD.
Click to expand...
Now the questions:
Click to expand...
1) Can I create 2 volumes (if volume is the right word) one 3x180 GB
RAID 5 for 360 GB of space (more or less) and the other 2x320 GB RAID
1/5 for additional 320 GB (Total 680 GB out of 1180)?
Click to expand...

If it is Linux software-RAID based an you do not fear partitioning
and configuring the RAID arrays yourself, this is possible and I have
done similar things in the past. The trick is not to use full
disks as basis, but partitions. Linux software RAID supports that.
Out of the box or with a hardware controller, you can typically
only do full-disk RAID.

2) If later I add a 4th HD, for example a 750 GB HD, can I upgrade the
system without losing data and without doing any external backup to a
2 volumes systems with one 4x180 GB RAID 5 for 540 GB of space and the
other 3x320 GB RAID 5 for additional 640 GB and eventually a volume
single HD of 250 GB (TOTAL 1430 GB out of 1930)
Click to expand...

Very likely not. The problem is not only extending the RAID array
(again Linux software RAID with a modern kernel can do it), but you
also need to extend the filesystem, which I think does currently not
work even under Linux.
3) If later I substitute the smallest HD with a 750 GB HD, can I
upgrade the system without losing data and without doing any external
backup to a 3 volumes systems with one 4x180 GB RAID 5 for 540 GB of
space, one 4 x320 GB RAID 5 for additional 960 GB and the other 2x250
for additional 250 GB (TOTAL 1750 GB out of 2500)
Click to expand...

See above.
If yes for all the questions, which NAS on the market allow me to do
this upgrade friendly?
Click to expand...

Out of the box: None. The Linux software-RAID based ones have
more flexibility, but you would have to use the ordinary RAID
management tools (mdadm).

I suggest you read up on Linux software RAID to get an idea
of what is involved.
Thanks a lot and sorry for the long message
Click to expand...

No problem. You should realize, that while from a user's
POV your expectations are entirely reasonable, the technology
is not there or only partially there.

Arno
 
If it is Linux software-RAID based an you do not fear partitioning
and configuring the RAID arrays yourself, this is possible and I have
done similar things in the past. The trick is not to use full
disks as basis, but partitions. Linux software RAID supports that.
Out of the box or with a hardware controller, you can typically
only do full-disk RAID.
Click to expand...

That's good. I also read that flex-raid technology in RND4250 could
allow this operation
Very likely not. The problem is not only extending the RAID array
(again Linux software RAID with a modern kernel can do it), but you
also need to extend the filesystem, which I think does currently not
work even under Linux.
Click to expand...

That's strange. I thought if I had an HD with only 0, the parity still
hold if I pass from 3x180 to 4x180. Then the controller could fill the
forth HD with data and update the parity.

I will have a look at linux RAID software...
So maybe it's better to start with a 2x500 and then upgrade the system
with other 500 GB HD (with x-raid on RND4250). The problem then is
that if I want to extend capacity I have to substitute all the four
HD.

Do you think with Windows home server could be a better solution?

My needs are
- 300+ capacity for picture, mp3 etc where I want redundacy
- backup of 2 laptop documents (100 GB each) where I don't need
redundancy since I have one copy on the laptop and another on the NAS

Thanks Maurizio
 
That's good. I also read that flex-raid technology in RND4250 could
allow this operation
Click to expand...
That's strange. I thought if I had an HD with only 0, the parity still
hold if I pass from 3x180 to 4x180. Then the controller could fill the
forth HD with data and update the parity.
Click to expand...

That is possible for some RAID solutions. But your partition size and
the filesystem in the partition will not get extended, and you end up
with just 180GB empty space at the end of the RAID array.
I will have a look at linux RAID software...
So maybe it's better to start with a 2x500 and then upgrade the system
with other 500 GB HD (with x-raid on RND4250). The problem then is
that if I want to extend capacity I have to substitute all the four
HD.
Click to expand...

And you still have to adjust the pratitioning and filesystem sizes.
Do you think with Windows home server could be a better solution?
No.

My needs are
- 300+ capacity for picture, mp3 etc where I want redundacy
- backup of 2 laptop documents (100 GB each) where I don't need
redundancy since I have one copy on the laptop and another on the NAS
Click to expand...

Extending RAID arrays really is more of an art today. I suggest you
plan something that will keep for some time and in the future
get something larger. E.g a 2x1TB RAID1 would probably keep
for 3 years or so for you. Then in 3 years you can get an additional
one.

Arno
 
Extending RAID arrays really is more of an art today. I suggest you
plan something that will keep for some time and in the future
get something larger. E.g a 2x1TB RAID1 would probably keep
for 3 years or so for you. Then in 3 years you can get an additional
one.
Click to expand...

Thanks a lot

Bye Maurizio
 
You might read up on ZFS & RAIDZ. It's kicking ass in a number of areas.

<http://en.wikipedia.org/wiki/Zfs>

I suspect you'd need to use it a networked file server, or run M$ as a
virtual machine.
Click to expand...

Thanks for the link.

Now I have to decide if save time and go for a ready made solution
like Acer Aspire Easy Store or save money but invest lot of time and
go for a home made solution

Bye Maurizio
 
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