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© Rakhesh Sasidharan

Elsewhere

[Aside] AD Sites, Subnets, Trusts, etc.

  • How Domain Controllers are Located Across Trusts – this is a delightful article. I don’t know why, but I simply loved the way the author presented the information. Very logically written. Wish I could write blog posts with such clarity.
    • Praise aside, it is a good article on how subnet and site definitions are used to find a Domain Controller closest to you, and especially how it works across forest trusts.
  • Using Catch-All subnets in AD – Wanted to know how catch-all subnets in AD Sites will interact with specific ones. This one explained it. The specific one takes precedence. Which is exactly what you want. :)

[Aside] SPNs

Trying to get people at work to clean up duplicate SPNs, and came across some links while reading about this topic. 

From the official MSDN article: A service principal name (SPN) is a unique identifier of a service instance. SPNs are used by Kerberos authentication to associate a service instance with a service logon account. This allows a client application to request that the service authenticate an account even if the client does not have the account name.

Basically when a client application tries to authenticate with a service instance and the domain controller needs to issues it Kerberos tickets, the domain controller needs to know whose password to use for the service instance – is it that of the server where this instance runs, or any service account responsible for it. This mapping of service -> service account/ computer account is an SPN. It’s of the format service/host:port and is associated with the AD account of the service account or computer account (stored in the servicePrincipalName attribute actually).

That’s all!

[Aside] DFRS links

Just putting these here as bookmarks to myself.

One of our DCs at work had the following DFSR warnings in the DFS Replication logs:

The DFS Replication service stopped replication on volume C:. This occurs when a DFSR JET database is not shut down cleanly and Auto Recovery is disabled. To resolve this issue, back up the files in the affected replicated folders, and then use the ResumeReplication WMI method to resume replication.

Additional Information:
Volume: C:
GUID: 56234A2C-C156-11E2-93E8-806E6F6E6111

Recovery Steps
1. Back up the files in all replicated folders on the volume. Failure to do so may result in data loss due to unexpected conflict resolution during the recovery of the replicated folders.
2. To resume the replication for this volume, use the WMI method ResumeReplication of the DfsrVolumeConfig class. For example, from an elevated command prompt, type the following command:
wmic /namespace:\\root\microsoftdfs path dfsrVolumeConfig where volumeGuid=”56234A2C-C156-11E2-93E8-806E6F6E6111″ call ResumeReplication

For more information, see http://support.microsoft.com/kb/2663685.

Sounded like an easy fix, so I went ahead and tried resuming replication as directed. That didn’t work though. Got the following:

The DFS Replication service stopped replication on the folder with the following local path: D:\SYSVOL_DFSR\domain. This server has been disconnected from other partners for 154 days, which is longer than the time allowed by the MaxOfflineTimeInDays parameter (60). DFS Replication considers the data in this folder to be stale, and this server will not replicate the folder until this error is corrected.

To resume replication of this folder, use the DFS Management snap-in to remove this server from the replication group, and then add it back to the group. This causes the server to perform an initial synchronization task, which replaces the stale data with fresh data from other members of the replication group.

Additional Information:
Error: 9061 (The replicated folder has been offline for too long.)
Replicated Folder Name: SYSVOL Share
Replicated Folder ID: xxxxx
Replication Group Name: Domain System Volume
Replication Group ID: xxxxxx
Member ID: xxxxx

Yeah, bummer!

Check out this Microsoft blog post for content freshness and the MaxOfflineTimeInDays parameter. You can’t simple remove SYSVOL from DFSR replication groups via the GUI as it is a special folder, so you have to work around. I found some forum posts and blog posts that suggested simply raising this parameter for the broken server to a number larger than the number of days its currently been offline (154 in the above case) and then resuming replication. I wasn’t too comfortable with that. What if any older changes from this server now replicate to the other servers? That could cause more damage than it’s worth. I don’t think this will happen, but why take a risk. What I really want is to force a replication onto this server from some other server. Do a non-authoritative replication basically. So I followed the steps in this article and that worked.

A non-authoritative sync is like a regular sync, just that it is rigged to let the source win. :p So all the existing files on the destination server are preserved. The event log gets filled with entries like these:

The DFS Replication service detected that a file was changed on multiple servers. A conflict resolution algorithm was used to determine the winning file. The losing file was moved to the Conflict and Deleted folder.

Additional Information:
Original File Path: D:\SYSVOL_DFSR\domain\Policies\{F4A04331-3C62-474A-A1CE-517F17914111}\GPT.INI
New Name in Conflict Folder: GPT-{4B7F4510-3C34-4A8A-A397-BC736AE5D9B6}-v55459.INI
Replicated Folder Root: D:\SYSVOL_DFSR\domain
File ID: {8189DA2F-DCBE-4755-A042-72154B648111}-v949
Replicated Folder Name: SYSVOL Share
Replicated Folder ID: 05ECDBE0-A0E6-4A9A-B5BE-7C404E323600
Replication Group Name: Domain System Volume
Replication Group ID: 46C8DB83-463F-459F-8785-DCB19231C52B
Member ID: 7A0E2DA6-4841-40A1-B02D-F5F341345B98
Partner Member ID: 7851F335-6824-4B0D-9978-5A5520ECD547

If you want to see where these files are now moved to check out this blog post. That post has a lot more useful info.

[Aside] Citrix VDI Best Practices for XenApp and XenDesktop 7.6 LTSR

This is an amazing document! Skimming through the PDF version and I am blown away. Some day when I have to make Citrix related decisions, this is the document I will be turning to. (Came across it via the Citrix blog, so thank you!)

There’s also a XenDesktop handbook but I haven’t read it yet. 

[Aside] PVS Caching

Was reading this blog post (PVS Cache in RAM with Disk Overflow) when I came across a Citrix KB article that mentioned this feature was introduced because of the ASLR feature introduced in Windows Vista. Apparently when you set the PVS Cache to be the target device hard disk, it causes issues with ASLR. Not sure how ASLR (which is a memory thing) should be affected by disk write cache choices, but there you go. It’s something to do with PVS modifying the Memory Descriptor List (MDL) before writing it to the disk cache, and then when Windows reads it back and finds the MDL has changed from what it expected it to be, it crashes due to ASLR protection. 

Any how, while Googling on that I came across this nice Citrix article on the various types of PVS caching it offers:

  • Cache on the PVS Server (not recommended in production due to poor performance)
  • Cache on device RAM
    • A portion of the device’s RAM is reserved as cache and not usable by the OS. 
  • Cache on device Disk
    • It’s also possible to use the device Disk buffers (i.e. the disk cache). By default it’s disabled, but can be enabled.
    • This is actually implemented via a file on the device Disk (called .vdiskcache).
    • Note: the device Disk could be the disks local to the hypervisor or could even be shared storage to the hypervisors – depends on where the device (VM) disks are placed. Better performance with the former of course. 
  • Cache on device RAM with overflow to device Disk
    • This is a new feature since PVS 7.1. 
    • Rather than use a portion of the device RAM that is not usable by the OS, the RAM cache portion is mapped to the non-paged RAM and used as needed. Thus the OS can use RAM from this pool. Also, the OS gets priority over PVS RAM cache to this non-paged RAM pool.
    • Rather than use a file for the device Disk cache, a new VHDX file is used. It is not possible to use the device Disk buffers though. 

The blog post I linked to also goes into detail on the above. Part 2 of that blog post is amazing for the results it shows and is a must read for these and the general info it provides (e.g. IOPS, how to measure them, etc). Just to summarize though: if we use cache on device RAM with overflow to device Disk, you get tremendous performance benefits. Even just 256 MB device RAM cache is enough to make a difference.

… the new PVS RAM Cache with Hard Disk Overflow feature is a major game changer when it comes to delivering extreme performance while eliminating the need to buy expensive SAN I/O for both XenApp and Pooled VDI Desktops delivered with XenDesktop. One of the reasons this feature gives such a performance boost even with modest amounts of RAM is due to how it changes the profile for how I/O is written to disk. A XenApp or VDI workload traditionally sends mostly 4K Random write I/O to the disk. This is the hardest I/O for a disk to service and is why VDI has been such a burden on the SAN. With this new cache feature, all I/O is first written to memory which is a major performance boost. When the cache memory is full and overflows to disk, it will flush to a VHDX file on the disk. We flush the data using 2MB page sizes. VHDX with 2MB page sizes give us a huge I/O benefit because instead of 4K random writes, we are now asking the disk to do 2MB sequential writes. This is significantly more efficient and will allow data to be flushed to disk with fewer IOPS.

You no longer need to purchase or even consider purchasing expense flash or SSD storage for VDI anymore. <snip> VDI can now safely run on cheap tier 3 SATA storage!

Nice!

A follow-up post from someone else at Citrix to the two part blog posts above (1 & 2): PVS RAM Cache overflow sizing. An interesting takeaway: it’s good to defragment the vDisk as that gives up to 30% write cache savings (an additional 15% if the defrag is done while the OS is not loaded). Read the blog post for an explanation of why. Don’t do this with versioned vDisks though. Also, cache on device RAM with overflow to device Disk reserves 2 MB blocks on the cache and writes in 4 KB clusters whereas cache on device Disk used to write in 4 KB clusters without reserving any blocks beforehand. So it might seem like cache on device RAM with overflow to device Disk uses more space, but that’s not really the case …

As a reference to myself for later: LoginVSI seems to be the tool for measuring VDI IOPS. Also, yet to read these but two links on IOPS and VDI (came across these from some blog posts):

[Aside] PVS vs MCS

Haven’t read most of these. Just putting them here for when I need ’em later.

[Aside] NetScaler – CLI Networking

Just putting these two here as a reference to myself (no idea why coz I am sure I’ll just Google and find them later when I need to :p)

As an aside (to this aside):

  • The NetScaler config is stored as ns.conf at /nsconfig
  • Older versions have a .0, .1, .2, etc suffixed to the filename. 
  • Backups are stored in /var/ns_sys_backup.
  • More info on backups etc

[Aside] Useful CA/ Certificates info

[Aside] NetScaler VPX Express limitations etc.

Reading about NetScaler VPX as we are looking at implementing VPX Express in our site as part of a POC. 

  1. VPX Express is limited to 5  Mbps (as opposed to say 1 Gbps for VPX-1000). 
  2. The license is free but you have to keep renewing annually.
  3. The Edition is NetScaler Standard. This and this are two links I found that explain the difference between various editions. 
    1. tl; dr version: Standard is fine for most uses. 
  4. The Gateway part supports 5 concurrent user connections. 
  5. You cannot vMotion or XenMotion VPX. 
  6. This is an excellent blog post on VPX, MPX, and others. Worth a read. 

[Aside] How to Secure an ARM-based Windows Virtual Machine RDP access in Azure

Just putting this here as a bookmark to myself for later. A good post. 

[Aside] NetScaler newnslog files

Some links to myself on the newnslog files (these are binary log files; high precision; need a tool called nsconmsg to view them). 

A typical format of the command is like this:

The <operation> can be one of these (this is just a copy-paste from nsconmsg -?):

The newnslog files are rotated every 2 days (or a certain number of events if I remember correctly). The older ones can be accessed by putting a path to that file (e.g. /var/nslog/newnslog.28.tar.gz in the command above). This will extract the file and show the logs. The Citrix page says we have to extract the logs first, but am guessing that’s old info. 

That’s all for now. Will add more to this post later …

[Aside] NetScaler SSL

Just putting in these links as bookmarks to myself for future. I kinda followed them while I was trying to change my NetScaler certs (kinda followed, coz I didn’t find these links when I Googled initially, so I just went ahead and figured it out by trying; but later I came across these and thought it would be a good idea to link them here). 

[Aside] How to quickly get ESXi logs from a web browser (without SSH, vSphere client, etc)

This post made my work easy yesterday – https://www.vladan.fr/check-esxi-logs-from-web-browser/

tl;dr version:  go to https://IP_of_Your_ESXi/host

[Aside] The Ultimate Guide To Being An Introvert – Altucher Confidential

I tweeted this link but then thought I should put it on my blog too mainly as a reference to myself. Sometimes I wander through my blog looking for wisdom and I hope to find this post then. A great read, especially if you are an introvert and view that/ have been told that it’s a bad thing. 

http://www.jamesaltucher.com/2017/04/ultimate-guide-being-introvert/

Read the full article (it is long); here’s an excerpt I liked. 

Being an introvert has nothing to do with being shy. Or being outgoing or not outgoing. Or being socially awkward.

All it means is that some people recharge when they are by themselves (introverts).

Other people recharge when they are interacting with many other people (extraverts) and most people are in the middle.

I lose energy very quickly when in a group of people. Getting invited to a party is horrible for me.

I say “no” to almost every social situation. Because I know they will take energy away from me doing the things I love.
If I’m giving a talk it’s no problem. Because I’m by myself on the stage. It’s one to many instead of me just one in a mess of people. I recharge on the stage.

[Aside] Windows Update tools

Wanted to link to these as I came across them while searching for something Windows Updates related.

  • ABC-Update – didn’t try it out but looks useful from a client side point of view. Free.
  • WuInstall – seems to be a client and server thing. Putting it here so I find it if ever needed in future. Paid.
  • Windows Update PowerShell Module – you had me at PowerShell! :0)
    • A blog post explaining this module. Just in case.