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Storage Design with Flash Storage. One Big LUN vs multiple smaller LUNS.

Traditionally, when storage design was done for VMware Environments, a lot of criteria had to be considered. This included

  • Number of Drives
  • Speed of Drives
  • Number of IOPS per each drive
  • RAID penalty
  • Write Penalty
  • Read Penalty
  • Scalability of the Array

But with the advent of all flash arrays (XIO, Pure, Nimble, Violin etc etc) a lot of these parameter no longer constraint the storage design for VMware environments. Each of the AFA offerings have their own RAID kind of technology, which pretty much  guarantees a very high resiliency to failure and data loss. Also with the new kind of Flash drives introduced (eMLC from memory), the consumer level SSDs are no longer used in AFAs. So now that the physical limitations on the drives have been eradicated, lets look at the next steps.

Queue Depth: 

Queue depth is a very misleading constraint, there are queue depths at each level, LUN, Processor, Array. So each physical enitity(or not so physical for CNAs and LUN) has an individual queue depth. How do we address this short coming? If there is a lot of IO being thrown at the Array, if its not able to process it, the queue is going to fill up.

If the host parameters are not set properly, it will start to fill up the HBA queue depth across the multiple LUNs that it has access to. Some of these parameters can be changed to ensure that the ESXi vmkernel process does things differently when using AFAs.

I’ve previously mentioned some parameters that need to be changed for XtremIO. I guess the same would apply for all the AFAs out there. Using ESXi with AFA and not changing advanced parameters to take advantage of AFA is like, buying a Ferrari to drive in Melbourne CBD. It only proves that you are an idiot, restricted by the ‘speed limit’.

OK But what about LUNs:

Now to the original question, One Big LUN vs Multiple smaller LUNS. Each decision has its own advantages and disadvantages, for example, choosing one Big LUN can give cumulative IOPS available across multiple storage nodes in AFA. So if one node provides 250,000 IOPS (random workload 50% read), then adding another node to it will enhance it to 500,00 IOPS. That single node provides more IOPS than a fully scaled and filled VNX 7500. Thats a lot of horsepower if you ask me.

The same can be said for multiple smaller LUNS, each LUN created is spanned (atleast in XtremIO AFAIK) across all the available nodes in the cluster. So you would still get the benefit of insane amount of IOPS for each decision.

Other Considerations:

There are other considerations that you will need to take into account when designing storage for VMware. To start with, workload consideration is a good one. Depending on the workload thats consuming all of these resources, you might want to provide a single big LUN or the application architecture might force you to use multiple smaller LUNS. One of my customers’ SQL Team is convinced that even on AFA, the data and the log LUN have to be separated on ‘spindles’. I explained about the lack of spindles and the redundancy/resiliency/availability aspect of AFA. After a long discussion, it was agreed that there would still be multiple LUNs created but all of them on the same 2 XIO node array. Not across the other 2 x 2 node XIO arrays that are available.

What about DR/SRM:

DR/SRM strategy doesn’t need to change significantly for SRM. I have always believed in providing the optimal number of LUNs for SRM for a mixed workload. Some applications might require a separate LUN (for a vApp for example). While some are happy to co-exist. It also comes down to the application owners, some application owners are adamant that the workloads should be maintained seperately, while others are happy to co-exist on the same LUN as long as their RTO/RPO requirements are met.

So in short, the answer is ” IT DEPENDS“. But my vote goes to multiple medium sized LUNs (10-12TB) :). This will provide the advantages of both big and small LUNS.

Whats your say ?

I’d appreciate the comments about this in the blog rather than on twitter, but then again both are social media so doesn’t matter.

Performance Tuning VDI Environment – My Opinion

This year is the “year of the VDI” as was last year and the year before that. There are very few environments which are as simple but still complex to design and manage as a VDI environment. vSphere has provided a lot of ways to virtualise the server workloads over the years and VMware View (Horizon View) has definitely given it the edge for deploying VDI environments.

There are people who swear by Citrix and there are people who swear by View, I am in the latter group (no surprises there). But there is one thing common between Citrix VDI (Xen Desktop) and VMware View deployments, if not designed and implemented carefully, they can both cause more issues than resolve. Typically, VDI is used to simplify patching OS (Windows) and still have control over the Corporate Data for growing number of people moving towards Macs and iPads for Corporate use. This is a good thing, generally. You relinquish the resources used by “corporate” machines and let people buy the machine that they are happy to use and you still control how they logon to corporate resources and manage the permissions on what they can and cant do.

One thing that a lot of people mis understand is the use for VDI and how they design it. Needless to say, VDI can be slow and cumbersome if not tuned correctly which affect the users perspective of VDI as a technology. A few things to look out for when designing VDI solutions using either Citrix or View:

  • If there are large number of Persistent users, ensure that the resources are in local cache mode, so that they can use the resources on thier local machine instead of hogging resources from the pool.
  • Create multiple pools based on user requirements, Power Users, Heavy Graphic Users, Kiosk users. They all have different requirements and expect different things from the VDI.
  • One size (image) doesnt fit all. If you have a large number of applications, make sure you can virtualise them. Virtualising applications moves the processing of the back end to the servers leaving VDI footprint small and applications run faster.
  • Pre-install (Pre-push) the most commonly used applications in the pool on the base image, patching the application and rolling back from a bad patch becomes easier.
  • Have a seperate cluster to house Heavy Graphic Users. This will eliminate the noisy neighbour problem with other non heavy users.
  • Ensure that all the replica images and base images are on the fastest disk available (FLASH FLASH FLASH)
  • Linked clones can be on slower disk, but if you can use fast disk use it.
  • Persistent Images can be on slower disk, especially if local cache is used, freeing up faster disk for linked clones.
  • Ensure that your vCenter server is not a single point of failure for all your VDI users ( especially when more than 2000 users).
  • If you are designing VDI for branch offices connected by WAN, PCoIP is probably the best option especially if you dont have WAN accelerators between locations.
  • User Disks can be on slower disk but this will impact the user logon experience so use the fastest slow disk you can (see what I did there).
Last but not the least:Dont forget to include the VDI enabling machines (Composer, Connection Server, PVS, MCS, etc etc) in your calculations for resource utilisation.Please feel free to comment and let me know what I have missed and I will include them..


Things that need to be changed on vSphere for Xtreme IO

Xtreme IO is the newest and fastest (well EMC say so) All Flash Array in the market. I have been running this in my “lab” running a POC which is quickly turning into a major VDI refresh for one of the clients. Having run throug the basics of creating storage and monitoring alerting etc in my previous posts., I am going to concentrate on what parameters we need to change in the vSphere world to ensure we get the best performance from Xtreme IO.

The parameters also depend on what version of ESXi you’re using, as Xtreme IO supports ESXi 4.1 + .

Without further delay, lets start.

Adjusting the HBA Queue Depth

We are going to sending a lot more IO through to the Xtreme IO array than you would to the traditional hybrid array. So we need to ensure that the HBA queue depth is allowing a lot more IO requests through.
You can find out the module by using the command

Step 1: esxcli system module list | grep ql (or lpfc for emulex)

Once you find out the module that is being used. The command below can be used to change the HBA queue depth on the server.

Qlogic – esxcli system module parameters set -p ql2xmaxdepth=256 -m qla2xxx (or whatever is the module from the command in Step 1.)

Emulex – esxcli system module parameters set -p lpfc0_lun_queue_depth=256 -m lpfc820 ( or whatever is the module from the command in Step 1)

Multi Pathing

If you are not going to use Powerpath, since its an active active X number of controllers array (yeah, i know its got 2 controllers per disk shelf so as of today you can scale upto 6 disk shelves per cluster so 12 controllers), we will be using Round Robin if using NMP.

The engineers who work with Xtreme IO recommend that the default number of iops be changed from 1000 to 1, yes “ONE”. So essentially you are sending an IO request to each controller in the cluster. I haven’t really seen any improvement in the performance by doing so but it is only a recommendation at the end of the day. If you see that you are not going to achieve any significant performance by doing so, the onus is on you to make that decision.

First, lets get all the volumes that’ve been configured on Xtreme IO.

esxcli storage nmp path list | grep XtremeIO

this will give you the naa.id of all the volumes that are running on XtremeIO.

Now lets set the policy to RR for those volumes.

esxcli storage nmp device set — device <naa.id> -psp VMW_PSP_RR (5.x)
esxcli nmp device setpolicy — device <naa.id > –psp VMW_PSP_RR (4.1)

You can also set the default path selection policy for any storage in 5.x by identifying the SATP and modifying it with the command

esxcli storage nmp satp set –default-psp=VMW_PSP_RR —satp =<your_SATP_name>

To set the number of IOs to 1 in RR,

esxcli storage nmp psp roundrobin deviceconfig set -d <naa.id> –iops 1 –type iops (5.x)

esxcli nmp roundrobin setconfig –device=<naa.id> –iops=1 (4.1)

Of course if you dont want to go change all of this, you can still use Powerpath.

Host Parameters to Change

For best performance we also need to set a couple of disk parameters. You can do this via GUI or the easier way via CLI (preferred).

Using GUI, set the following parameters Disk.SchedNumReqOutstanding to 256 & Disk.SchedQuantum to 64

Note: If you have non Xtreme IO volumes on these hosts, they may lead to over stress on the controllers and cause performance degradation while communicating with them.

Using Command line in 4.1, set the parameters using

esxcfg-advcfg -s 64 /Disk /SchedQuantum
esxcfg-advcfg -s 256 /Disk /SchedNumReqOutstanding

to query that its been set correctly, use

esxcfg-advcfg -g /Disk /SchedQuantum
esxcfg-advcfg -g /Disk /SchedNumReqOutstanding

You should also change the Disk.DiskMaxIOSize from the default of 32767 to 4096. This is because XtremeIO reads and writes by default in 4k chunks and thats how it gets the awesome deduplication ratio.

In ESXi 5.0/5.1 you can set the SchedNumReqOutstanding by using

esxcli storage core device set -d <naa.id> -O 256

In vSphere 5.5 you can set this paramter on each volume individually instead of configuring on per host.

vCenter Server Parameters

Depending on the number of xBricks that are configured per cluster, the vCenter server parameter
config.vpxd.ResourceManager.maxCostPerHost needs to be changed. This adjusts the maximum number of full cloning operations.

One xBrick Cluster – 8 (default)
Two xBrick Cluster – 16
Four xBrick Cluster – 32

Thats the end of this post. Please feel free to correct me if I’ve got any commands wrong.


Recommendation (as per AusFestivus’ comment):  EMC recommend that PP be used for best performance. But it always comes down to the cost constraints and how much the client wants to spend.  In my opinion, PP is more like “nice to have for best performance without tinkering”. But if you can keep tinkering and changing things to get the best performance out, you can do without PP.

Xtreme IO – Part 2 – Monitoring, Alerting and Security

This is part 2 of the 2 part Xtreme IO Blog post. You can find the first one here.

We will cover the basics of Monitoring and Security in Xtreme IO in this post. Please remember this is not a deep dive of the newest AFA. You should still consult the Official EMC product Documentation for up to date information.


XMS can be locked down to use either local accounts or ldap authenticated accounts. There are default accounts that are pre-configured on the XIO. However, it is possible to change the default passwords of the root, IPMI, tech and admin accounts.

There are 4 user roles that are available on the XMS.

  • Read-Only
  • Technician – Only EMC Technician should use this
  • Administrator – All access
  • Configuration – Cant edit, delete or add users


LDAP Authentication

The XtremIO Storage Array supports LDAP users’ authentication. Once configured for LDAP authentication, the XMS redirects users’ authentication to the configured LDAP for Active Directory (AD) servers and allows access to authenticated users only. Users’ XMS permissions are defined, based on a mapping between the users’ LDAP/AD groups and XMS roles.





The XMS Server LDAP Configuration feature allows using a single or multiple servers for the external users’ authentication for their login to the XMS server.

The LDAP operation is performed once when logging with external user credentials to an XMS server. The XMS server operates as an LDAP client and connects to an LDAP service, running on an external server. The LDAP Search is performed, using the pre-configured LDAP Configuration profile and the external user login credentials.

If the authentication is successful, the external user logs in to the XMS server and accesses the full or limited XMS server functionality (according to the XMS Role that was assigned to the AD user’s Group). The external user’s credentials are saved in the XMS Cache and a new user profile is created in the XMS User Administration configuration. From that point, the external user authentication is performed internally by the XMS server, without connecting to an external server. The XMS server will re-perform the LDAP Search only after the LDAP Configuration cache expires (cache expiration default value is 24 hours) or at the next successful external user login if the external user credentials were removed from the XMS Server User Administration manually.

LDAP user authentication can be configured and managed via either GUI or CLI.


Monitoring can be done from both a physical level and a logical level using the new Xtreme IO (XIO) Management Server (called XMS hereafter). In the current environment, I only have one xBrick for testing. So my XMS is only managing a cluster of 1 xBrick. At this point in time, a single XMS can only manage one cluster (although this might change in the next few code revisions) with a maximum of 8 xBricks. The unofficial word from my colleague in EMC is that this will be updated to support upto 16 xBricks. I have deployed the XMS as a VM afterall why would anyone want a physical server these days except to run ESXi.. right ?

Physical Monitoring

Monitoring on the physical devices in the XIO cluster is very easy. Click on the “Hardware” link in the application and it will be show all the physical components of the cluster (including the infiniband switches) but since I only have one xBrick, that is all thats shown.
Hover the mouse over the components and the health status of that component will be shown. This goes down the level of each disk in the 25 SSD DAE and also the disks in the controllers. So all aspects can be seen either wholistically or individually.






We can also check the back side of the unit including the cabling between various components. If we have an Infiniband switch, we can also check the cabling between the controllers and the infiniband switches.



That takes care of the physical monitoring of the components.

Alerts & Events

To look at the alerts and events on the XIO, click on the Alerts & Events link. This will show us all the alerts that are currently unacknowledged on the XIO and also the various events that happened. We can clear the logs if required when diagnosing any problem if it does get filled up.






Log Management

It is possible to use SMTP, SNMP or syslog to provide alerting and log management. We can do this in Administration tab, under Notification.

To configure SMTP, we need to enter the following details (Select SMTP) and click Apply






To configure SNMP, enter the Community name and server details and click Apply.






To configure Syslog, enter the syslog server details and click Apply.






This concludes my 2 part Introduction to Xtreme IO. Thank you for reading.


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