Posts Tagged ‘deduplication’

Scripted CIFS Shares Migration

March 8, 2018

I don’t usually blog about Windows Server and Microsoft products in general, but the need for file server migration comes up in my work quite frequently, so I thought I’d make a quick post on that topic.

There are many use cases, it can be migration from a NAS storage array to a Windows Server or between an on-premises file server and cloud. Every such migration involves copying data and recreating shares. Doing it manually is almost impossible, unless you have only a handful of shares. If you want to replicate all NTFS and share-level permissions consistently from source to destination, scripting is almost the only way to go.

Copying data

I’m sure there are plenty of tools that can perform this task accurately and efficiently. But if you don’t have any special requirements, such as data at transit encryption, Robocopy is probably the simplest tool to use. It comes with every Windows Server installation and starting from Windows Server 2008 supports multithreading.

Below are the command line options I use:

robocopy \\file_server\source_folder D:\destination_folder /E /ZB /DCOPY:T /COPYALL /R:1 /W:1 /V /TEE /MT:128 /XD “System Volume Information” /LOG:D:\robocopy.log

Most of them are common, but there are a few worth pointing out:

  • /MT – use multithreading, 8 threads per Robocopy process by default. If you’re dealing with lots of small files, this can significantly improve performance.
  • /R:1 and /W:1 – Robocopy doesn’t copy locked files to avoid data inconsistencies. Default behaviour is to keep retrying until the file is unlocked. It’s important for the final data synchronisation, but for data seeding I recommend one retry and one second wait to avoid unnecessary delays.
  • /COPYALL and /DCOPY:T will copy all file and directory attributes, permissions, as well as timestamps.
  • /XD “System Volume Information” is useful if you’re copying an entire volume. If you don’t exclude the System Volume Information folder, you may end up copying deduplication and DFSR data, which in addition to wasting disk space, will break these features on the destination server.

Robocopy is typically scheduled to run at certain times of the day, preferably after hours. You can put it in a batch script and schedule using Windows Scheduler. Just keep in mind that if you specify the job to stop after running for a certain amount of hours, Windows Scheduler will stop only the batch script, but the Robocopy process will keep running. As a workaround, you can schedule another job with the following command to kill all Robocopy processes at a certain time of the day, say 6am in the morning:

taskkill /f /im robocopy.exe

Duplicating shares

For copying CIFS shares I’ve been using “sharedup” utility from EMC’s “CIFS Tools” collection. To get the tool, register a free account on You can do that even if you’re not an EMC customer and don’t own an EMC storage array. From there you will be able to search for and download CIFT Tools.

If your source and destination file servers are completely identical, you can use sharedup to duplicate CIFS shares in one command. But it’s rarely the case. Often you want to exclude some of the shares or change paths if your disk drives or directory structure have changed. Sharedup supports input and output file command line options. You can generate a shares list first, which you can edit and then import shares to the destination file server.

To generate the list of shares first run:

sharedup \\source_server \\destination_server ALL /SD /LU /FO:D:\shares.txt /LOG:D:\sharedup.log

Resulting file will have records similar to this:

:Projects ;Projects ;C:\Projects;

Delete shares you don’t want to migrate and update target path from C:\ to where your data actually is. Don’t change “@Drive:E” headers, they specify location of the source share, not destination. Also worth noting that you won’t see permissions listed anywhere in this file. This file lists shares and share paths only, permissions are checked and copied at runtime.

Once you’re happy with the list, use the following command to import shares to the destination file server:

sharedup \\source_server \\destination_server ALL /R /SD /LU /FI:D:\shares.txt /LOG:D:\sharedup.log

For server local users and groups, sharedup will check if they exist on destination. So if you run into an error similar to the following, make sure to first create those groups on the destination file server:

10:13:07 : WARNING : The local groups “WinRMRemoteWMIUsers__” and “source_server_WinRMRemoteWMIUsers__” do not exist on the \\destination_server server !
10:13:09 : WARNING : Please use lgdup utility to duplicate the missing local user(s) or group(s) from \\source_server to \\destination_server.
10:13:09 : WARNING : Unable to initialize the Security Descriptor translator


I created this post as a personal howto note, but I’d love to hear if it’s helped anyone else. Or if you have better tool suggestions to accomplish this task, please let me know!


NetApp SnapMirror Optimization

May 31, 2013

gzipSnapMirroring to disaster recovery site requires huge amount of data to be transferred over the WAN link. In some cases replication can significantly lag from the defined schedule. There are two ways to reduce the amount of traffic and speed up replication: deduplication and compression.

If you apply deduplication to the replicated volumes, you simply reduce the amount of data you need to be transferred. You can read how to enable deduplication in my previous post.

Compression is a less known feature of SnapMirror. What it does is compression of the data being transferred on the source and decompression on the destination. Data inside the volume is left intact.

To enable SnapMirror compression you first need to make sure, that all your connections in snapmirror.conf file have names, like:


Then use ‘compression=enable’ configuration option to enable it for particular SnapMirror:

connection_name:src_vol dst_system:dst_vol compression=enable 0 2 * *

To check the compression ration after the transfer has been finished run:

> snapmirror status -l

And look at ‘Compression Ratio’ line:

Source: fas1:src
Destination: fas2:dest
Status: Transferring
Progress: 24 KB
Compression Ratio: 3.5 : 1

The one drawback of compression is an increased CPU load. Monitor your CPU load and if it’s too high, use compression selectively.

NetApp Operations Manager Efficiency Dashboard

May 30, 2013

Fancy tool to report storage returns from deduplication and thin-provisioning, as well as various breakdowns of storage utilization. Efficiency Dashboard is installed as a script into the DataFabric Manager and can be accessed at this URL: http://um-server-hname:8080/dashboard.html.

Here is an example of the Efficiency Dashboard report (click to enlarge):



Storage Utilization shows Total/Used capacity. Raw Capacity Breakdown has more detailed utilization figures, such as Fixed Reserve (amount of space reserved for Kernel, WAFL Reserve, Checksums, etc). You can quickly find out from the Unused Reserve Capacity section if you have any volumes or LUNs left thick-provisioned. Storage Efficiency and Efficiency Return Breakdowns have detailed info on various storage efficiency returns, such as deduplication, thin-provisioning, RAID-DP, etc.

If you need to present a colourful report of thin-provisioning and deduplication returns to the customer, then I recommend to try this tool.

Unexpected Deduplication Impact on VMware I/O Latency

May 28, 2013

NetApp deduplication is a postponed process. During normal operation Data ONTAP only calculates hashes for the data blocks. Actual deduplication is carried out off-hours as per configured schedule. Hash calculation doesn’t affect performance in most cases. I talked about that in my previous post. NetApp states in its documentation that deduplication is a low-priority process:

When one deduplication process is running, there is 0% to 15% performance degradation on other applications.

Once I faced a situation when deduplication was configured to be carried out during business hours on one of the volumes. No one noticed that at some point volume run out of space and Data ONTAP wasn’t able to perform deduplication from that time. Situation became worse when Data ONTAP was upgraded from version 7.3.2 to 8.1.0. Now during deduplication filer tried to upgrade the fingerprint metadata to a new version at 15:00 every day with the message: “Fingerprint is being upgraded” and failed. It seems that the metadata upgrade is a very resource-intensive process and heavily affects I/O latency.

This volume was not a VMware datastore, but it sit on the same aggregate together with the several VMFS LUNs. Here what happened to the VMware I/O latency every day at 15:00 (click to enlarge):


I deleted the host name and the datastores names from the graph. You can see the large latency spike, which won’t turn yourVMs into kernel panic, but it’s not the thing you would want your production environment to experience every day.

The solution was simple. After space was increased on this volume, deduplication metadata upgrade performed successfully and problem went away. Additionally, deduplication was shifted to off-hours.

The simple lesson to learn: don’t schedule deduplication during the day, you never know what could possibly go wrong.

NetApp Reallocate

May 24, 2013

top-defragment-2The smallest addressable block of data in Data ONTAP is 4k. However, all data is written to volumes in 256k chunks. When data block which is bigger than 256k comes in, filer searches for contiguous 256k of free space in the file system. If it’s found, data block is written into it, if not then filer splits the data block and puts it in several places. It’s called fragmentation and is familiar to everyone from the times, when FAT files ystems were in use. It’s not a big issue in modern file systems, like NTFS or WAFL, but defragmentation can help to solve performance problems in some situations.

In mostly random read/write environments (which is quite common these days) fragmentation has no impact on performance. If you write or read data from random places of the hard drive it doesn’t matter if this data is random or sequential on the physical media. NetApp recommends to consider defragmentation for the applications with sequential read type of workload:

  • Online transaction processing databases that perform large table scans
  • E-mail systems that use database storage with verification processes
  • Host-side backup of LUNs

Reallocation process uses thresholds values to represent the file system layout optimization level, where 4 is normal and everything bigger than 10 is not optimal.

To check the level of optimization for particular volume use:

> reallocate measure –o /vol/vol_name

If you decide to run reallocate on the volume, run:

> reallocate start –f /vol/vol_name

There are certain considerations if you’re using snapshots or deduplication on volumes. There is a “-p” option, to prevent inflating snapshots during reallocate. And from version 8.1 Data ONTAP also supports reallocation of deduplicated volumes. Consult official documentation for additional information.

Further reading:

TR-3929: Reallocate Best Practices

NetApp Deduplication in a Nutshell

May 12, 2013

NetApp-Dedupe2NetApp uses Write Anywhere File Layout (WAFL) filesystem which is a key for NetApp’s efficient snapshot technology. If you’re already familiar with how snapshots are implemented in Data ONTAP, then understanding underlying mechanisms of deduplication is simple. Filer calculates hash for each data block it receives and preserves this in the form of metadata on the volume level. Then according to deduplication schedule (usually on weekends), filer runs metadata processing and for each duplicate hash changes data pointer to the original block of data.

Since for each data block filer needs to calculate hash on the fly, it has its penalty. On systems with CPU loaded by less than 50% performance impact is negligible. For heavily loaded systems, where CPU is nearly 100% busy, performance impact can be around 15%. For high-end 6000 systems penalty can jump up to 35% for random writes. Heavy sequential read operations can also suffer from deduplication, because read operations can be rerouted in random way across physical storage, depending on where the original data block actually is. In general, deduplication has low impact on system performance. But you can’t use it blindly and should keep in mind that in particular cases it can slow down your storage system.

Deduplication configuration is pretty simple. First of all, you need to activate deduplication on particular volume:

> sis on “targetvol”

If you already have data on the volume, you need to scan it. Otherwise, it won’t be deduped. It’s a common mistake. Deduplication is a low priority task, but keep in mind, however, that it can slightly impact your storage performance when done during business hours, especially if you run deduplication for several volumes simultaneously.

> sis start -s “targetvol”

To show the status of deduplication for particular volume:

> sis status “targetvol”

To see the deduplication schedule:

> sis config “targetvol”

And the most pleasant command to find out how much data you’ve saved:

> df -s “targetvol”

If you want to undo deduplication, first switch it off and then undo it using the following commands:

> sis off “targetvol”
> priv set advanced
*> sis undo “targetvol”
*> priv set

I, personally, was able to achieve 40% deduplication rate for VMware VMFS datastores, which is rather impressive, considering these were mixed OS + application data LUNs.

As a final note, I would like to point out, that deduplication is suitable only for environments with high percentage of similar data. VMware is a good example of it. You won’t get any significant deduplication ratio for swap file volumes, Exchnage mailboxes or Symantec Enterprise Vault which is already deduped.

Further reading:

TR-3958: NetApp Data Compression and Deduplication Deployment and Implementation Guide: Data ONTAP 8.1 Operating in 7-Mode