Spindles / SAN

[netmgr001]

i have a question regarding the placement of VHD's and the creation of CSV's in a small hyper-v setup you'd find in a medium sized school where you'd maybe have two or max three virtualised hosts either clustered or just splitting of workload without
clustering, i'm still trying to get my head around CSV's and the use of the different type of VHD's against RAW disk mapping, but it seems that for simplicity you'd want to mirror how you'd setup your physical servers based on the application type in terms of RAID levels.

So if you've got a starter fibre or iscsi array with 12 disks, can you have 8+1 for RAID-5, and then have a two-disk RAID 1 for parent partition boot from SAN (if that's supported), and then that leaves one disk left over for hot spare ? But then how would you carve up the raid-5 into LUNs if you were to virtualize the usual suspects like exchange, SIMS, file serving. as long as you happy to stick with RAID-5 for those apps and not need to separate out for log files and RAID 1+0. Just do it based on the size of the LUN required ? dedicate a LUN for each application. Or just have one big LUN per RAID group.

[Dave_O]

The principle here is KISS. Forget all this boot from SAN stuff just makes things too complicated. I wouldn't do RAW disk mapping as some backup technologies don't support them. You don't say what disk types you have SATA, SAS etc. As I think I said before, in a school this absolute performance not really an issue.

Create LUN (s) as big as possible (supported by your OS) and stick your servers on it. The problem as I found when you create a lot of small LUNs is that no matter how well you plan, servers grow and you'll run out of space. At least with one/two big LUNs you have space to grow.

[oxide54]

you want to be careful of scsi reservations creating one big lun. its a double edged sword, hudge vdisk/arrays/etc will give you loads of IOPs because of the spindle count, but you don't want something I/O heavy swamping the rest of your stuff.

def agree probably not worth raw device mapping.

personally i disagree over the performance thing (really depends what you have running), I do agree you don't need stupidly expensive ssd's though.

oh and get vmware and a san that supports VAAI

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started perfmon'ing the VM's IOPS this week so far today the staff file server gets the most hits, be interesting to see how it pans out by the end of the week.

[Dave_O]

1. Are SCSI resevations relevant for fibre?
2. With a potential of 50,000+ IOPS I don't think contention will be an issue
3. Having watched the V7000 IOPs at device, controller and disk level over a long period of time each day, I have seen no spikes or experienced performance issues. This is working with full load (45VMs ranging from file servers, Exchange, SQL, SIMS, Sharepoint, SCCM, Lync etc including some 20 Windows 7 machines from VMWare View)
4. VAAI - dabbled with this but stopped. Not sure I want VMWare making decisions about VM storage placement, still like to think I have some input into this!

[oxide54]

1. Are SCSI resevations relevant for fibre?

Yes, but not with VAAI

[oxide54]

@Dave_O what raid level are you running ? 10?

[oxide54]

VAAI not about VMWare deciding where VM's go, it offloads SAN to SAN copies directly to the SAN to avoid copying SAN to ESX then ESX to SAN when it could just go SAN to SAN. Plus not locking the LUN when a SCSI reservation would normally lock the LUN but doing it at a block level.

this is a pretty good explanation

What is VAAI

[Dave_O]

Posted earlier in thread but again

Pool 1 - 1 volume, 8 drives RAID 1+0 2.2Tb usable space. IBM easy tier enabled - this uses the 2 SSDs to cache "hot" blocks, does this automatically over time.
Pool 2 - 1 volume, 12 drives RAID 6 5.6Tb usable space. (Fileservers, misc inc web servers etc - mainly read some write)
Pool 3 - 1 volume, 12 drives RAID 6 5.6Tb usable space. (Fileservers, SCCM, misc inc web servers etc)
Pool 4 - 1 volume, 6 drives RAID 5 2.6Tb usable space. (Misc inc web servers etc - mainly read)

[Dave_O]

Sorry got the wrong thing I thought VAAI was the storage consolidation capability of VSphere. When would this be used in a normal situation?

[oxide54]

Storage VMotion, Provisioning new VM's from templates. Snapshots.

These are some examples of VMFS operations that require locking metadata:

From

VMware KB: Analyzing SCSI Reservation conflicts on VMware Infrastructure 3.x and vSphere 4.x

Creating a VMFS datastore
Expanding a VMFS datastore onto additional extents
Powering on a virtual machine
Acquiring a lock on a file
Creating or deleting a file
Creating a template
Deploying a virtual machine from a template
Creating a new virtual machine
Migrating a virtual machine with VMotion
Growing a file, for example, a Snapshot file or a thin provisioned Virtual Disk
Any software that updates itself regularly, particularly system utilities like antivirus programs and operating system updates. (**** SERIOUSLY ????? WHERE???)


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[Dave_O]

*Creating a VMFS datastore
*Expanding a VMFS datastore onto additional extents
*Powering on a virtual machine
*Acquiring a lock on a file
*Creating or deleting a file
*Creating a template
*Deploying a virtual machine from a template
*Creating a new virtual machine
Migrating a virtual machine with VMotion (host or storage?)
Growing a file, for example, a Snapshot file or a thin provisioned Virtual Disk
Any software that updates itself regularly, particularly system utilities like antivirus programs and operating system updates

Looking at these the ones starred don't happen very often nor do they take very long. So what are the advantages?

[oxide54]

Host VMOTION would benefit from reducing LUN locking, Storage VMotion would benefit from the SAN copying as well.

Snapshots lock the LUN every 16mb of growth. not sure on thin provsioned .

i think the last item they listed is related to thin provisoned disks.

for me the SAN to SAN copy is the reason. also reduces CPU load on the ESX box as well.

its also not so much about speeding up provisoning a VM for the administrator, but not degrading the users performance as a result.

[Dave_O]

SAN to SAN copying I do once every 5 years (when I decomission a unit), funnily enough just last month! I know it can mean LUN to LUN on the same box. I'll have a look at it, I know the V7000 supports it.probably have a mess around with it at the weekend

[Dave_O]

Well I'll be! Just checked VAAI is on, supported and working and I didn't know! The wonders of modern technology eh! I'll give you a thank you for that one (even though technically nothing has changed - just makes me feel better knowing more)

[oxide54]

maybe why your not seeing any performance problems with lun locking???