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gbrot
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navisphere / cx300 raid group management

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I've inherited a cx300 array to manage recently and I'm a little new to it and navisphere so I've got some questions.  I was about to purchase more drives to add some space but I've noticed 3 different RAID groups where there is quite a lot of 'free capacity', unallocated into LUN's.  I've also found a large LUN that is not mapped to a host...  Is there any reason someone would do this??  At the time of purchase that must have been thousands of dollars worth of RAID 10 space that has been unallocated for years.

So my questions are... is there a LUN set aside for CX300 software perhaps, or some reason for not allocating space, besides not needing the space? 

If I can use that unallocated space can I expand a drive in windows without having to remove and replace the contents?  (I suppose I'd have that question if I were purchasing new hd's as well)

Thanks!

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Dev Mgr
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Re: navisphere / cx300 raid group management

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Assuming your OS supported extending partitions (e.g. Windows 2000 and later, Linux, but not Netware or ESX 3.x), to grow a LUN, there are 2 options; MetaLUN expansion, or a LUN migration.

Here is a short description of your options and some of the pros and cons of each.

 

MetaLUNs add a 2nd LUN to the existing LUN so that the OS thinks it's 1 'larger' LUN.

Advantages:

- can be done quick (once the 2nd LUN has finished binding) if using the concatenation option

- very flexible (when using the concatenation option, the 2nd LUN can be a different raid type, different size, in a different raid group (but cannot be a different disk type (FC vs SATA))

- can also be used for performance (striping option, but for this best practices is: different raid group with the same number of drives, the same raid type, the same drive type, same spindle speed and the same LUN size)

Disadvantages:

- the performance on a MetaLUN is limited by the slowest common denominator (starting with an 8+1 disk raid 5 and adding a metalun component from a 2+1 disk raid 5 could reduce overall performance of the LUN

- MetaLUN striping takes time

- generally 'uncancellable/unrevertable' once started

 

LUN migration migrates a LUN to a different LUN (the destination will have all data wiped on it and cannot be in a storage group (i.e. in use by a server)).

Advantages:

- you can migrate from anything (raid type and/or disk type) to anything else, as long as it's the same size or larger (this last part is where the expansion part comes in)

- if it's still running and you realize you made the wrong choice, you can cancel the migration and you can fix the mistake and start over (will have to rebind the destination LUN if needed)

- the change in data location is transparent/invisible to the server (few exceptions to this rule may exist when running Unix though)

Disadvantages:

- time consuming

- you need enough free space (e.g. when migrating a 100GB LUN to somewhere else, you need the complete destination space available; i.e. another 100GB (or more))

 

 

 

 

Member since 2003

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Dev Mgr
5 Rhenium

Re: navisphere / cx300 raid group management

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The array does use some space on the first 5 drives (about 6.5 to 7GB on each of those drives). This space is used for the OS of the storage processors and some other features. This space isn't visible in Navisphere though; it just shows those 5 drives as having a bit less available disk space.

 

Was that large LUN maybe at one point assigned to a server that has been decommissioned since then (and the LUN pulled out of the storage group)?

 

What flare version are you running? To check -> right click the CX300, select properties, go to the software tab and look for the flare version. It should be formatted something like 02.xx.300.5.xxx. I'm asking for this as it influences your options to expand and migrate LUNs.

 

 

Member since 2003

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gbrot
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Re: navisphere / cx300 raid group management

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The flare version is 02.24.300.5.006

I guess the extra space wasn't needed at first, and then was forgotten with staff changes.  It looks like it's always been directly attached to one server with the same drive letters, from the documentation I've found.

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Dev Mgr
5 Rhenium

Re: navisphere / cx300 raid group management

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Assuming your OS supported extending partitions (e.g. Windows 2000 and later, Linux, but not Netware or ESX 3.x), to grow a LUN, there are 2 options; MetaLUN expansion, or a LUN migration.

Here is a short description of your options and some of the pros and cons of each.

 

MetaLUNs add a 2nd LUN to the existing LUN so that the OS thinks it's 1 'larger' LUN.

Advantages:

- can be done quick (once the 2nd LUN has finished binding) if using the concatenation option

- very flexible (when using the concatenation option, the 2nd LUN can be a different raid type, different size, in a different raid group (but cannot be a different disk type (FC vs SATA))

- can also be used for performance (striping option, but for this best practices is: different raid group with the same number of drives, the same raid type, the same drive type, same spindle speed and the same LUN size)

Disadvantages:

- the performance on a MetaLUN is limited by the slowest common denominator (starting with an 8+1 disk raid 5 and adding a metalun component from a 2+1 disk raid 5 could reduce overall performance of the LUN

- MetaLUN striping takes time

- generally 'uncancellable/unrevertable' once started

 

LUN migration migrates a LUN to a different LUN (the destination will have all data wiped on it and cannot be in a storage group (i.e. in use by a server)).

Advantages:

- you can migrate from anything (raid type and/or disk type) to anything else, as long as it's the same size or larger (this last part is where the expansion part comes in)

- if it's still running and you realize you made the wrong choice, you can cancel the migration and you can fix the mistake and start over (will have to rebind the destination LUN if needed)

- the change in data location is transparent/invisible to the server (few exceptions to this rule may exist when running Unix though)

Disadvantages:

- time consuming

- you need enough free space (e.g. when migrating a 100GB LUN to somewhere else, you need the complete destination space available; i.e. another 100GB (or more))

 

 

 

 

Member since 2003

gbrot
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Re: navisphere / cx300 raid group management

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Thanks!  That's a lot of good info.

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