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need to purchase a server for virtualization. confused about 10K RPM disks and near-line SAS 7.2k RPM. do not require any redundancy for data hence RAID0 will do. choose disks 10K SAS for OS array and slower 7.2 K drives for data, does this config require two controllers? (PERC 6i) need approx 2 TB of data space, am confused by number of drives that a controller can handle and the form factor (2.5 inch vs 3.5 inch), since real estate is no problem rack or tower is fine

experts please answer. thanks in advance

updates: mid-range performance is acceptable, the server hosts approx 25+ VM's(windows only) and may have few SQL Server DB.....no heavy i/o, but occasionally.

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DELL PE 2970 looks good, but dont seem to configure more than 4 300GB 10K SAS? By your answer PERC 6i can handle both SATA and SAS ? –  John-ZFS Jan 21 '10 at 13:15
    
I think you want to flip-flop your OS and VM arrays. You want the VM array to be the fastest. After booting, the ESX OS should be in RAM and does not need to hit the hard drive for OS tasks, only for VM tasks. –  Scott Lundberg Jan 21 '10 at 15:02
    
sounds interesting, but an array for just ESX ? Hypervisor should need less than 2GB max....it may have control over the vmfs formatted array.Not sure what –  John-ZFS Jan 21 '10 at 15:15

2 Answers 2

up vote 3 down vote accepted

lets separate the issues:

SAS vs NL-SAS is very simple. While SAS drives are the proper SAS (i.e. SCSI drives with a serial connector and access protocol), NL-SAS is really a SATA disk with a SAS connector and access protocol. The advantage of NL SAS vs SATA is in the connector and protocol, because while you can use SATA disks connected to SAS controllers, you will suffer performance hits in addition to the disk slowness, because there will always be a protocol conversion between SCSI (the protocol SAS uses) and ATA (the protocol IDE and SATA use) So in the end, SAS vs NL-SAS is just the matter of RPMs, while SAS vs SATA was RPMs plus overhead


3.5" vs 2.5" is even easier - you choose between larger (in size, not capacity) and cheaper drives, and smaller and more expensive drives. The caveat of the larger and cheaper ones is the fact that you can fit much less of those on a backplane. I have two IBM 1U pizzaboxes in my server room, one can hold up to two 3.5" drives, and the other - up to 6 2.5" drives. This can not only give you more capacity, but can bring you up to a higher spindle count, which is a major factor when you need disk performance (and with VMs you probably will)


PERC6i will be able to handle whatever you put in that server, just create several raid arrays.


I would strongly advise against raid-0 no matter what the requirements are. It is simply too risky, especially if in case of a failure you'll end up restoring or recreating several VMs, instead of a single physical machine

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1. do you mean NL-SAS is same as SATA or worse but no way near SAS? the fastest NL-SAS is 7.2K RPM only..? 2. for future scalability choose 2.5 form factor drives? are the 300GB 10K 2.5 SAS the best economy? iam looking at only DELL PE –  John-ZFS Jan 21 '10 at 13:36
    
1. NL-SAS is sata technology, minus the protocol conversion overhead. so it wil work faster than sata on a sas controller, but slower that sas on a sas controller, because the rpms are lower 2. correct. if you want more drives - use 2.5" 3. don't know about economy, you should consult your Dell sales rep and maybe ask to talk to a TSR as well - they are usually very god and technical –  dyasny Jan 21 '10 at 13:58

Using the faster disks for the OS and slower bigger disks for the data is a good idea, you won't require two controllers but may have to be careful with your server selection.

Any new server with SAS disk support will likely either have a 3.5" or 2.5" hotswap drive bay. 2.5" disks mean you can fit in more disks but as redundancy doesn't seem to be an issue (how about performance?) you might be better off going for 3.5" bays so you can get higher capacity 7.2k RPM 3.5" disks for storing the data.

Bear in mind while you might not require additional redunancy RAID 0 will actually increase the likelihood of data loss.

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