VNX Raid Group and Pool General Questions

Question

I'm deploying my first VNX (5300) in the next week or so, and have gone through the Quickstart training, but am still fuzzy on a couple of critical details regarding configuration options. I would really appreciate any help with the following:

1.) Vault Drives - The first 4 drives in my DPE are used for the VNX OEs (understood); however, I get the impression that the ability to use capacity of these drives depends on whether you opt to use RAID Groups or Pools. I have read on this forum that if you provision traditional RAID groups, only a small portion of the vault drives is reserved for the VNE OEs for block and file, and the rest is usable capacity. Conversely, were I to choose to create pools on my DPE, those drives would be completely unavailable for data use. I get this from the EMC VNX best practice document on storage provisioning (page 94):

"The maximum number of drives in a storage pool is storage system model-dependent. It is the maximum number of drives for the model, less the four drives of the system drives (Only entire drives may be provisioned in pools)".

Can someone confirm this please? And if this is the case, is it standard practice when planning on using pools as opposed to the 16-drive-max RAID Groups, to just purchase 4 of the smallest available drives for vault usage?

2.) The system I have been shipped includes 24 600G 15k SAS drives (15 in the DPE, and 9 in the first DAE). My client would like the performance of RAID 10 with these drives. In this case, I obviously cannot create a single RAID group given the 16-drive limitation, so I am considering using a pool. This creates a problem, because if the answer to my first question is "yes, that is correct", then I only have 20 drives available for the pool, which is not a number evenly divisible by 8 without remainder. According to the best practice document, this is not recommended because the pool would be made up of 2 8-drive RAID 10s and a single 4-drive RAID 10 (correct?). If I were to designate 2 drives as hotspares, this would be 2 8-drive RAID 10's and a 2-drive RAID 10 in the pool (correct)? Is this that big of a deal from a performance perspective? What are the scalability implications? Say, for instance, I wish to add another DAE in the future with 8 more drives in it, and add them to the pool, would this then mean that my pool was made up of the first two 8-drive groups, the single 4-drive group, and then a newly added 8-drive group in the second DAE?

3.) Can FAST VP be added at any time to create a 2-tiered pool? If I create this homogenous pool now, may I later add some NLSAS or Flash drives in a new DAE and enable FAST VP?

4.) If the answer to my first question was "no, vault drives can also be members of a pool", then I guess there is no problem because I will then have three 8-drive RAID 10's to make up the pool (though I should probably add a hotspare).

Thanks in advance!

Rainer_EMC · Answer

Correct – the first four drives cannot be used in a pool

You can use them as (additional) traditional raidgroups

Even with traditional raidgroups you shouldn’t mix them with the other disks in a raidgroup since they are smaller

Yes - the pool will make automatic decisions regarding raidgroup sizes

You could “trick” it by first creating a pool with 6 disks R10 and then adding 6 more disks

This way it would have to create two 6-disk R10

As far as performance goes – if the LUN is fully provisioned it will be “split” into 1GB slices

Data that is residing on a slice that is on a 2-disk R10 will obviously have a different performance than one that is on a 8-disk R10

Yes, FAST VP can be added as a license at any time

Of course it only works on pools and not on traditional raidgroups

I would suggest to look at the best practices and reference architectures for the application you are deploying and then decide wether you want to use pools or traditional raidgroups.

Traditional raidgroups give you more control – pools more flexibility and ease of use

We usually don’t see that many configs with all RAID10 – typically its R10 for specific LUNs and R5 for the rest

Rainer

dynamox · Answer

Rainer_EMC wrote:We usually don’t see that many configs with all RAID10 – typically its R10 for specific LUNs and R5 for the rest i have two VNX5700 with all RAID10, 15K drives pool for Citrix XenServer implementation. I am ok to take 10% penalty performance hit by using pools, don't have to pull my hair by engineering traditional raid groups.

Robert_Barrett · Answer

Thanks so much for the info. Ticking the pool into creating RGs of a specified size is a great idea, thanks! Some followup:

1.) When the VNX ships, I'm assuming the OS is loaded on the vault drives --correct? I wasn't a part of the pre-sales process but it appears as though nobody considered that because my DPE is completely full of the 15k SAS drives that I am supposed to use for luns. If the vault drives are not to be used for data, I wonder why it wasn't communicated that there should be a smaller (perhaps less costly) set of disks in the first four positions? Do you know if I can buy some other drives for the vault after its been shipped?

2.) Just of curiousity, since pools are made of individual raid groups, does that mean there is potential to be able to lose more than one drive in the pool, depending on which internal RG it's in? So if I setup a pool of 10 disks in RAID 5, that would create two 5-disk RG's. I could lose one in each internal group and still be fine, correct?

Robert_Barrett · Answer

What 10% performance hit are you referring to?  Between RAID 5, 6, and 10 -- 10 is leaps and bounds higher performing.  Write penalty is 2 for RAID 10, 4 for RAID 5, and 6 for RAID 6....

dynamox · Answer

overhead of using pools (thick LUNs)  vs traditional raid groups. I guess more metadata to manage on pool LUNs, results in higher CPU utilization on SPs..

Robert_Barrett · Answer

Great, thanks!

I haven't seen an answer yet to the vault drives question, but if it turns out I'm not able to swap those out, and I'm sitting on 4 600gig 15k SAS drives used for nothing other than the VNX OE, I'm curious what thoughts would be on using those drives to create a RAID group and use luns on that group for my VMWare ESXi installations (I'm booting from SAN).

dynamox · Answer

general recommendation is to not use those for anything i/o intensive.  I think ESXi boot LUNs would be a good candidate to use that space, ESXi installation is so tiny and once it's up everything is loaded into memory, i mean you can run ESXi from a USB stick.

Rainer_EMC · Answer

Thats fine then

You know what you are doing and I’m sure you’re building the pool with multiples of the optimal R10 raidgroup size

I would also recommend to use fully provisioned LUNs

Most customers just dont want to pay fort he R10 capacity overhead any longer

Rainer_EMC · Answer

1) yes the OS is pre-installed and the first four drive and you cannot change that (i.e. re-install yourself) 2) yes

Sundar107 · Answer

we are having DPE with block OE(Not having Warranty, bought from vendors)...and we want to unified system only .

my question is that

If i purchase 4 vault drive that contains Unified OE Pre-Installed or need to purchase whole DPE with unified

Rainer_EMC · Answer

@Sundar107 wrote:

we are having DPE with block OE(Not having Warranty, bought from vendors)...and we want to unified system only .

my question is that

If i purchase 4 vault drive that contains Unified OE Pre-Installed or need to purchase whole DPE with unified

A Unified VNX system able to provide NAS service also requires other hardware like control station, data movers, cables,....

I would suggest to contact the vendor you bought it from for help - I doubt that even with all the correct parts you will be able to put it together, reset the config and re-install it without professional help

VNX

VNX Raid Group and Pool General Questions

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