Dynamic FS/RAID5 questions

[MrChunks]

I'm trying to figure out if this is a really bad idea or not.

Basically, I want to add a file server to my home network (2-3 machines accessing it at once, serving/recording media/data) but I want it to be expandable.

Say, I start out with a RAID5 array in software, running under linux. I have 2 questions relating to the expansion of this box (while maintaining a "flat" appearance to the users)

First: is it a bad idea to "expand" a raid5 array, as in, add a new disk to it? Will it grow like that? Or am I stuck with what I start with (say, 4x400gb disks to start, and I want to add a 5th)

Second: Say I have those same 4x400gb RAID5 disks, and want more space. But I still want it as 1 "partition" for ease of organization. Can I create ANOTHER RAID5 array (another 4x400gb, or bigger depending on what's available) and then use the linux file system to encompass BOTH of the two arrays, thus making 8 physical drives, 2RAID5 arrays, into 1 single partition?

Would the second scenario present a significant risk to my data in the event of hardware failure?

It feels very much like i'm putting all my eggs in one basket with any of these ideas (even though RAID should be somewhat fault tolerant)

 

[underdone]

First: is it a bad idea to "expand" a raid5 array, as in, add a new disk to it? Will it grow like that? Or am I stuck with what I start with

I don't know of any software raid with online capacity expansion. But i do know that some of the high end raid controllers support this.

is it a bad idea to "expand" a raid5 array, as in, add a new disk to it? Will it grow like that? Or am I stuck with what I start with

The more discs that you add to an array the higher the likelyhood of one of them failing. I'm not totally sure what amount of discs in an array would warrant trying to do raid 6.

Can I create ANOTHER RAID5 array (another 4x400gb, or bigger depending on what's available) and then use the linux file system to encompass BOTH of the two arrays, thus making 8 physical drives, 2RAID5 arrays, into 1 single partition?

Like i said previously if you use a high end controller that supports online capacity expansion you can do this. Some even support this accross multiple adapters but thos are ridiculously expensive. I'm not sure if there is another software way of doing this through linux, kind of like dynamic disks or something like that.

 

[Dew]

Like i said previously if you use a high end controller that supports online capacity expansion you can do this. Some even support this accross multiple adapters but thos are ridiculously expensive. I'm not sure if there is another software way of doing this through linux, kind of like dynamic disks or something like that.

If by high and and ridiculously expensive you mean the $260 Highpoint RR2320(8-port), then yes. It fits all the features you mentioned.

 

[The Hunter]

Well, I haven't done this in practice, but I've spent some time researching it (thinking of doing more or less the same idea as you).
I've mostly been looking at EVMS, which looks like a really good comprehensive solution for managing both the software raid and filesystem components in one nice interface.

From what I've read, yes you can expand it by putting in an additional disk. You have to unmount the array, and it can take some time, but it's perfectly doable. If you're using reiserfs or xfs, you need to do a little trick to get the filesystem to expand too, but its well documented in the faq and doesn't seem terribly hard.

 

[drizzt81]

Say, I start out with a RAID5 array in software, running under linux. I have 2 questions relating to the expansion of this box (while maintaining a "flat" appearance to the users)

First: is it a bad idea to "expand" a raid5 array, as in, add a new disk to it? Will it grow like that? Or am I stuck with what I start with (say, 4x400gb disks to start, and I want to add a 5th)

I have heard rumors that LSR supports online capacity expansion. I am sure that it depends on what kernel/ LSR version you are using and possibly how it has been set up. U_M is the local guru for this

 

[unhappy_mage]

LSF? Linux Software Fraid?

EVMS supports expansion, and in the (very limited!) test I did, it worked perfectly in expanding a 3-disk raid 5 to 4 disks and keeping the data intact.

 

[drizzt81]

LSF? Linux Software Fraid?

EVMS supports expansion, and in the (very limited!) test I did, it worked perfectly in expanding a 3-disk raid 5 to 4 disks and keeping the data intact.

the F was part of Software, I just omitted the raid