CX4 Series Storage help

EMC's CX-series do not support SAS drives.

I would also suggest you call your salesrep and have him/her engage their technical salesrep (TSR) to figure out your requirements. 30TB raw space is not the same as 30TB usable space.

A few notes about the CX4-series/CX4-960;

- the first enclosure (bus 0 enclosure 0) has to use FC drives

- the first 5 drives in the first enclosure (bus 0 enclosure 0 disk 0 to bus 0 enclosure 0 disk 4) lose 67GB for the OS of the array and these drives are best avoided for high IO data.

- write cache is mirrored between the 2 storage processors, so don't think you'll actually get 32GB of cache; the CX4-960 maxes out at about 13GB of write cache (16GB per storage processor, of which about 2.5GB is for the OS)

- EMC Clariion arrays (AX, CX, CX3, and CX4-series) max out at 16 disks in a raid group, but you could use the MetaLUNs capability to 'merge' LUNs together to reach larger sizes

- each enclosure can hold up to 15 drives; per enclosure these have to either all be FC or all be SATA

Thanks for the return Dev Mgr!

I was wrong! The CX4-960 does not work with SAS drives, only SATA, FC and Flash!
If I use FC disks to 300GB 15Krpm with Raid5 and 15 disks per storage module, I need 8 expansion modules for 30TB of storage, right?
You know which PDU should I use this for storage?
Thanks again!

Do you need 30TB usable space or raw space? If 30TB raw is your requirement, you'd need 100 x 300GB drives, which is 7 enclosures fully loaded.

If you want 30TB usable space, it'll depend on your desired raid setup to determine how many enclosures you need (30TB in a raid 10 requires a lot more drives than multiple 16-disk raid 5's).

Dev Mgr,

I need 30TB of usable space in storage and I will probably use Raid5.
But what did not discover is which PDU should I use to connect CX4-960. The rack will be Dell, but I need to inform the specifications of the PDU. You know which PDU should use by default?
Thank you.

You'll want to ask your salesrep/TSR about the PDU. The CX4-960 does require 200-240V, 110/120V isn't supported.

Each 300GB drive is about 268GB usable. If we go with the maximum number of disks (that an EMC Clariion array can do) in a raid 5, we get 16-disk raid 5's. This would yield about 4020GB in usable space per raid 5. To get to 30TB (30 x 1024GB), you'd need 8 of these raid 5's.

So, after skipping the first 5 drives, you need 8 x 16 (300/15) drives, which is 128 drives. Then we add 5 hotspares for this quantity of drives. So we're looking at 133/15 = 8.87, and therefor 9 enclosures. This still doesn't account for the flare drives, which are 0.33 of an enclosure.

So, you would need:

- the CX4-960

- the DAE-OS (first 5 drives can be any FC drives you want as lose 67GB on them, so we'll just not count them towards the 30TB and the other 10 drives can be blanks if you want)

- 9 DAEs fully loaded with 300/15 FC drives.

Note: this doesn't yield optimal performance though; EMC recommends 4+1 or 8+1 drives in a raid 5 for optimal performance. That would change the numbers and add another enclosure possibly (though if the DAE-OS has 10 300/15 drives after the first 5 drives, those could help prevent the need for one more DAE).

Good afternoon Dev Mgr!

You have no idea how much this helps me, thanks!
However, I still have a query about the storage controllers. The CX4-960 has 2 controllers, right? And each of these controllers has 16GB of cache (nominal value), right? That´s right?
Thank again.

The CX4-960 indeed has 2 controllers, and each controller has 16GB memory (not cache). The OS on the controller takes about 2.5GB of this memory, leaving about 13-13.5GB of memory that you can allocate to any split between write and read cache (as the array isn't as dependent on read cache for it's performance, usually it's recommended to use about 2 MB/LUN for read cache (be a bit liberal, so maybe a minimum of 50MB for read cache, unless you go over 25 LUNs) and give everything else to write cache.

The write cache is mirrored between the controllers, so if you have 13GB for write cache, you cannot 'double' this number because you have 2 controllers, as both controllers have to have the exact same data in write cache (like a raid 1 of 2 drives only gives you 1 drive's worth in space, but you need 2 drives to make that raid 1).

Ok Dev, I understand ....
So it's impossible have to 16GB of cache per controller because the operating system of each controller occupies about 2.5 GB of cache memory.
But in this case, the CX4-480 has 8GB of cache for each controller and I need to 32GB in total.
Thanks again Dev, your help was crucial!
best regards!

The CX4-480 has 8GB RAM per controller, and then also loses about 2.5GB, leaving you with ~5.5GB to allocated to read and write cache.

Why are you so focused on having 32GB write cache? The CX4-480 is a very solid/fast system, and the CX4-960 is even more of a performance monster, even with 'just' 13GB write cache.

Dev

I am devoted to a technical specification to meet a government procurement and the specification requires the storage has a total of 32GB of cache, 16GB per controller. Only for this reason that I'm looking for the CX4-960, otherwise i would use the CX4-480, understand?

Thanks again Dev!

Best Regards!