Re: Upgrade raid0 to raid1

On 24 Lis, 02:47, General Schvantzkoph <schvantzk...@xxxxxxxxx> wrote:
On Fri, 23 Nov 2007 16:36:37 -0800, Kedarius wrote:
On 23 Lis, 22:41, General Schvantzkoph <schvantzk...@xxxxxxxxx> wrote:
On Fri, 23 Nov 2007 13:13:38 -0800, Kedarius wrote:
Hi,
I would like to ask, whether there are any possibilites how to
upgrade running raid0 to raid1.
I have two 2GB flash drives running as raid0 and I would like to
change it to two 4GB flash drives running RAID1 without stopping the
array. Is this somewhat possible?

Radek

Plug in the other two drives, configure them as RAID1 and then copy the
contents of the old drives to the new ones.

RAID0 and RAID1 perform two separate functions, RAID0, otherwise know
as striping, increase your bandwidth. RAID1, otherwise known as
mirroring, replicates the data on two drives to provide redundancy. If
you have more that two drives then you can combine the two functions in
a RAID5 array. However with just two drives your choices are 0 or 1 and
they are not compatible. If you pull one drive on a RAID1 and replace
it with another then you can rebuild the RAID set. If you pull one
drive from a RAID0 you have nothing be cause the data is spread across
both drives.

Just curious, why are you doing RAID with FLASH drives? FLASH drives
are great for moving data around but I'm not sure I would want to use
them as my main storage. FLASH drives have very slow write times, and
they also have a limited number of write cycles. In cameras, phones and
MP3 players this doesn't matter because they are fast enough and you do
very few writes to any particular location. I'm assuming you are using
them for some very low power application, but I would think that a
single drive would be best for that.

I know that I can move data by copying files. And I think this will be
the only one option but I was curious whether there is some possibility
doing this without stopping the RAID. Some magic with raid upgrading
(i.e. to raid10, etc :-)
We are using flash drives as / partitions for some of our servers. The
data and /var partitions are mounted from iSCSI drive. We've also tested
speed of these drives and we were able to achieve 15-20MB/s for
sequential write and read. The main reason for this is that we have a
lot of same hardware in custom made blade cases and two iSCSI servers
with a lot of capacity. The blades does not need HDD (in fact they are
only motherboards and PSU on a metal plate :-). We can easily move/
duplicate/etc. the flash images and the actual systems are independent
on the hardware. Deployng new server means copying prepared flash image
to new flash drives, changing hostname, IP, root pasword and booting on
new HW.
We use flash drives in raid1 so we can replace one in case of failure or
when flash drives reaches its maximum writes count. Unfortunatelly in
this one case customer insisted on buying two 2GB drives and striping
them because 4GB drives were much more expensive than two 2GB then. And
the server was experimental so downtime was no problem. And of course
the server has moved from experimental to production since and now he
would like to avoid downtime. And I was curious if this is possible....
Next step would be mirroring flash drives to iSCSI server and maybe
removing flash drives completely but for now we are rather happy with
this solution. And customers too, becasue they buy for example 2x500GB
HDD and can share it between 5 servers each with 100GB mirrored disk
capacity.

Are you putting /tmp and /var on the iSCSI drives? Using flash drives for
the OS is fine but using them for /var isn't a particularly good idea
because that's where the OS writes all of it's temporary files.

Yes. The data, /var and various other "high traffic" directories are
on iSCSI. /tmp is usually tmpfs or is from iSCSI server too.
.