Louwrentius

I'm responsible for a file server with about 5 terrabytes of data. The file server is based on Windows 2008 R2. I've noticed extreme memory usage on the server. After a reboot, it slowly builds up until almost all RAM memory is consumed.

So I googled around and found this post and it turned out I had the same exact issue.

I've confirmed with the tool 'RAMmap' that NTFS metadata is the issue. Microsoft also created a blog post about this.

The author of the first article resolved the issue by adding more RAM memory. But with 16 GB already assigned, I was not to happy to add more memory to the virtual file server, eating away on the RAM resources of our virtualisation platform.

I could never find a root cause of the issue. In that case, you need to obtain the 'Microsoft Windows Dynamic Cache Service'. This application allows you to configure how large the medata caching may grow.

Please note that this services is not a next-next-finish installation. Follow the included Word document with instructions carefully and configure a sane memory setting for your server. I limited the cache to half the RAM available to the server and this works out well.

If you are considering implementing DFS replication, consider using Windows 2012 R2 because DFS replication has been massively improved. It supports larger data sets and performance has dramatically been improved over Windows 2008 R2.

I've implemented DFS replication to keep two file servers synchronised. Click here if or there you want to learn more about DFS itself.

With DFS, I wanted to create a high-available file server service, based on two file servers, each with their own physical storage. DFS replication makes sure that both file servers are kept in sync.

If you setup DFS, you need to copy all the data from the original server to the secondary server. This is called seeding and I've used robocopy as recommended by Microsoft in the linked article.

Seeding is not mandatory. You can just start with an empty folder on the secondary server and just have DFS replicate all files. I've experienced myself that DFS replication can be extremely slow on Windows 2008 R2.

Once all files are seeded and DFS is configured, the initial replication can still takes days. Replication times are based on:

1. the number of files
2. the size of the data
3. the performance of the disk subsystems of both source and destination

Note: windows 2012 R2 improves DFS replication dramatically, only more reason to upgrade your file servers to 2012 R2 or higher.

If you seed the files, DFS will not transfer files if they are identical, thus this saves bandwidth and time. DFS checks if files differ based on their hash. So even if you seed all data, the initial replication can take a while.

On our virtualised platform, the initial replication of 2.5 GB of data consisting of about five million files took about a full week. To me, that is not a very desirable outcome, but once the initial replication is done, there is no performance issue and all changes are nearly instantly replicated to the secondary server.

For the particular configuration I've setup, the performance storage subsystem could contribute to the slow initial replication.

To speed up the replication process, it's important that you install the latest version of robocopy for Windows 2008 R2 on both systems. There is a bug in older versions of robocopy that do not properly set permissions on files. This results in file hash mismatches, causing DFS to replicate all files, nullifying the benefit of seeding.

Hotfixes for Windows 2008 R2: Hotfixes for Windows 2012 R2:

To verify if a file on both servers has identical hashes, follow these instructions

If you've checked a few files and assured that the hashes are identical, it's ok to configure DFS replication. If you see a lot of Event ID 4412 messages in the DFS Replication event log, there probably is an issue with the file hashes.

At work we have a couple of HP MSA P2000 G3 SANs. These are entry-level SANs that still seem to have almost all features you might want from a SAN, except for official SSD-support.

It seems that the new MSA 2040 adds support for SSDs and also provides 4 GB cache per controller instead of the somewhat meager 2GB of the P2000.

Anyway, a very nice feature of the MSA P2000 G3 is the fact that the management interface also provides a well-documented API that allows you to collect detailed stats on subjects like:

• Overall enclosure status
• Reports on failed drives
• Controller CPU usage
• IOPs per controller
• IOPs per vdisk
• IOPs per disk

Thomas Weaver has written a Nagios plugin that does that: it collects this information and in turn you can graph it with pnp4nagios.

In more recent firmware updates HP has added support to monitor read and write I/O latency per vdisk. Latency is an important indicator for application-level performance so I was quite happy with that.

As the plugin by Thomas did not support reading these parameters yet, I spend some time implementing this check and submitted this new version of check_p2000_api.php back to Thomas.

Read Latency of a RAID 6 array

Write Latency of a RAID 6 array

You will notice that the write latency of this disk array is very high at times, which seem to indicate that this vdisk is taxed too much with too many I/O-requests.

I'd like to thank Thomas Weaver for writing this plugin, I think it's very useful.