Highly Reliable Systems: Removable Disk Backup & Recovery

Monthly Archives: July 2017

Alternative to RAID1 Mirroring -Using DeltaSync

July 26th, 2017 by

High-Rely’s DeltaSync is a feature designed as an alternative to RAID1 mirroring for very large hard drives. It should not be confused with the Microsoft protocol of the same name.   DeltaSync is a high speed incremental copy from one drive to another.  It can be set to copy (resynch)  to create a “seed disk”  or it can be set to kick off and re-sync when a drive is swapped.  It can also be set to continuous (similar to the way our mirroring works) or even scheduled to happen daily at a certain time.  When set to “continuous” the Netswap operating system monitors the file I/O on the master disk for changes and when a file is written to and closed it immediately writes a copy of the new or changed file to the destination.  This is known as a true “Continuous Data Protection” (CDP) solution because updates happen based on any file I/O rather than based on a periodic schedule.    If files were copied on a tight schedule, say every 15 minutes, that would be “near CDP”.

The reason DeltaSync was created was that re-mirroring large multi-terabyte drives can sometimes take longer than 24 hours.  This is mainly a problem for 8TB drives and above.  Block level re-mirroring on a Netswap with stand alone hard drives is typically 300-500 Gigabytes per hour.  So an 8TB drive at 300GB/Hour might take 26.6 hours. Although RAIDPacs re mirror faster (about 2x the speed) they are also bigger  so a 16TB RAIDPac will remirror in a similar time frame.  By switching to a fast file synch only files that have changed since the drives were last synced are copied over, speeding the process considerably.  DeltaSync does not use Rsync or any other copy program available under Linux.  It uses low level file I/O to achieve copy speeds similar to mirroring.  The performance of this copy is very fast.  With any file based copy lots of small files will be slower than larger files but file transfer speeds approaching those of block level mirroring can be achieved.

Figure 1 Chose Properties on primary drive from Disk Menu

Setting up DeltaSync – An Alternative to RAID1 Mirroring

You will need at least 2 formatted drives to setup a DeltaSync.  From the Disk menu select properties button on the drive you want to be the primary as shown in Figure 1.

Figure 2 shows that DeltaSync drives must be shared in NAS mode (because when in iSCSI mode the disks are under the control of the iSCSI host machine and are unavailable to the Netswap OS).  At the bottom of the disk properties screen you can drop down the DeltaSync Settings menu.  You select this primary drive as the “source” of the DeltaSync data and choose between One Shot, One Shot Scheduled, One Shot Manual, Continuous, Continuous Scheduled, or Continuous Manual.

  • One Shot – Run once and stop

    Figure 2 Most DeltaSync jobs will be setup as continuous

  • One Shot Scheduled – Start at a specified time
  • One Shot Manual – Start when triggered by an Action URL or VBScript program (see Disk Tools).
  • Continuous – Sync and then continuously keep disks in sync
  • Continuous Scheduled – Start sync at specified time and then continuously keep disks in sync
  • Continuous Manual – Start when triggered by an Action URL or VBScript program (see Disk Tools) and then keep disks in sync.

Figure 3 First disk now shows as a DeltaSync Source

The most typical setting will be “Continuous”,  as that mimics the behavior of a set of mirrored hard drives except replicating at the file level. In Continuous mode the file system watches for I/O and as soon as it sees a new file or change to a file and the file is closed, it immediately copies the file to the target disk.  Once you select that Save and go back to the disks menu to see that the primary disk is now showing status of “DeltaSync Source” as shown in Figure 3.

Figure 4 – the second disk is setup as the destination

Figure 5 – Successful DeltaSync Setup

Now Choose Properties button on the second disk to set it up as a target as shown in Figure 4.  Figure 5 shows the disk status after saving.  Note that Disk 2 indicates it is a DeltaSync Destination for Disk1.   You should be able to prove the Deltasync is working by copying files to disk 1 using it’s UNC path.  All files copied should almost immediately show up on Disk 2.  Note that files deleted on disk 1 will similarly be deleted on disk 2 when setup in continuous mode.


Posted in Blog

Scheduled Mirroring on the NetSwap Can Protect against Ransomware

July 25th, 2017 by

Scheduled Mirroring and Ransomware

Scheduled Mirroring is a feature that is unique to Netswap backup appliances.  It is intended to allow the user to periodically mirror a drive to create an “air gap” without physically having to pull a drive and put it on a shelf.  In many ways, this is better than a real time mirror.   The real time mirror works well for protection against hard drive failures.  Delayed or Scheduled mirroring covers an even more common scenario:  of ransomware or other corruption that can creep into the backup (and a real time mirror) before it is discovered.  By having a copy of data from 1 week or several days ago, the enterprise protects themselves against fast moving Cryptolocker type ransomware or other new “zero day”  viruses.

Scheduled Mirroring

Figure 1. Create a Mirror from 2 drives

To setup scheduled mirroring you first need 2 hard drives.  Simply selected the “Disks” Menu along the side of the interface to get started with all these options.  We previously formatted two 4TB drives. As shown in Figure 1.  Figure 3 shows you won’t get the  “mirror schedule” button until you create a RAID 1 set.  In figure 2 we have clicked the “Create RAID Disk button,  chosen the 2 drives, and selected drive 1 to be our master.

Scheduled Mirroring

Figure 2 Creating a Mirror set

Scheduled Mirroring

Figure 3 How to get Mirror Schedule Button

Now choose the “Mirror Schedule” button that will appear next to one of the  two hard drives.   The “Disk Mirror Schedule” menu  pops up that will allow you specify how frequently you want to schedule the mirror as shown in Figure 4.

Scheduled Mirroring

Figure 4 – A typical setup is Mirror 1 time per week

Scheduled Mirroring

Figure 5 – A mirror schedule 2 minutes into future for testing

Since block level mirroring proceeds at 150-400 Gigabytes per hour make sure you allow enough time for a mirror to complete before removing media.  For example, re-mirroring 4TB drives takes around 10 hours.  We think once per week is a good period to have a point in time snapshot so in this example we’ve chosen Friday at 11pm.  However, if you’d like to you can re-mirror every night.  To test scheduled mirroring you might try to set the time for 2 minutes forward from the existing time, and tell it to go every day as we’ve done in figure 5.

Notice in Figure 6 that after we set the scheduled time the main menu will show the mirror as “degraded”.  This is because, in theory it always will be degraded with scheduled mirroring except during the period of time it’s actually rebuilding the mirror, when the status will be rebuilding.

Scheduled Mirroring

Figure 6 Normal Status of Scheduled Mirror is “Degraded”

Figure 7 Shows that when we wait for the scheduled time, the Netswap kicks off a re-mirroring job.

Scheduled Mirroring

Figure 7. Schedule time hits and re-mirroring starts

Here are some of the schedule options available to you:
Mirror Frequency
Select to specify that the disk should be attached to the mirror disk continuously.
Continuous with Scheduled Redundancy Check
Select to specify that the disk should be attached to the mirror disk continuously and that a mirror redundancy check be performed on the scheduled below. The mirror redundancy check verifies that the mirror is intact (both disks contain the same data) and corrects any errors found if possible.
Select to specify that the disk should be mirrored on the schedule specified below.
Every <n> hour(s)
Select to schedule the disk to be mirrored every <n> hours starting at a specific time. For example, every 3 hours starting at 09:00 am.
Every <n> day(s)
Select to schedule the disk to be mirrored every <n> days starting at a specific date and time. For example, every 2 days starting on 07/16/12 at 17:15.
Every <n> week(s)
Select to schedule the disk to be mirrored every <n> weeks on specific days of the week at specific times starting on specific date. For example, every 1 week on Monday at 06:00, Wednesday at 06:00, and Friday at 19:00 starting on 07/16/12.
Every <n> month(s)
Select to schedule the disk to be mirrored every <n> months on specific days of the month at specific times starting on a specific date. For example, every 1 month on the 1st and 15th at 06:00 starting on 07/16/12.

Note that it is normal for a scheduled mirror set to always be in “degraded” set.  Check the History to view the log that shows that the mirroring is happening per your schedule.  The mirror set will be broken as soon as the mirror completes and return to degraded status.  This is the normal operation.

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How to do Bare metal restore with Windows Backup using a NAS drive

July 18th, 2017 by

The question about how to do a bare metal restore is more of a software issue than a Netswap hardware issue but essentially it’s just a matter of attaching to the Netswap NAS via UNC path during the restore.  Here are more details:

First, it is important to note that “bare metal restore” from a NAS is easier with 3rd party programs such as Storagecraft, Acronis, Arcserve, VEEAM and the like.  This is why some experienced administrators or those who have tight Recovery Time Objectives (RTO’s less than a few hours) spend money for 3rd party solutions.  They are expensive but more robust. The second observation is that a bare metal restore is usually easier and faster when, during the initial setup, you first load the  Windows Hypervisor (included free with Windows 2012 and 2016) and then load the Windows OS as a single VM under that hypervisor.  This gives maximum flexibility.

Having said this, it is possible to do bare metal restore to native server hardware using the Windows backup program.  The default method of doing a bare metal restore is to boot the server from the Windows install media (this might be a CD or a usb key but must be the same windows version you are trying to recover).   Or you can hit F8 at boot time if the Windows installation is still on the disk but not working right.  Preparing an emergency boot USB key or CD, having them stuck right to side of server, and testing in advance is always a good idea.

Once you’ve launched the Windows Recovery environment there are a few steps:  specify language settings, and then click Next. Click Repair your computer. Setup searches the hard disk drives for an existing Windows installation and then displays the results in System Recovery Options. If you are recovering the operating system onto separate hardware or a machine with a blank hard drive (due to hard drive failure), the list should be empty (there should be no operating system on the computer). Click Next. On the System Recovery Options page, click System Image Recovery. This opens the Re-image your computer page. Select one of the options to pick an image.   “Use the latest available system image is the usual recommended restore point.

Click Advanced to browse for a backup in a remote shared folder on the network and provide the Universal Naming Convention (UNC) path to the backup (on the Netswap share),  In rare cases it may be necessary to load NIC drivers if the server is non-standard so it’s best to have network driver available in advance on your emergency boot media.  This is because the driver needs to be present in local system. You cannot install a driver from the network and, instead, need to provide a local path to the .inf file to install a driver so make sure it’ s on the CD or usb key in advance. Click Next.  Specify the location as something that looks like  \\Netswap-21\Mirrorset1 and follow the bouncing ball to restore the image.  You will have to reboot the server at the end.

These steps are provided in more detail here:


If time allows I would recommend running through a complete backup and subsequent restore before putting the server into production so you have all the pieces in place.

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