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Limitations of the Backup to Cloud Operation

  • This article is for Windows only

Carbonite Safe Server Backup (CSSB) allows users to perform backups to disk only, backups to cloud only, or backups to both disk and cloud. The Backup to Cloud operation has a few limitations and drawbacks, when compared to the other backup types. The limitations are technical and largely related to the power and speed of the machine that runs CSSB.

CSSB recommends that the Backup to Disk and Cloud be used whenever possible. It is generally faster and more stable than a Backup to Cloud only.

The following limitations could affect the Backup to Cloud operation:

Note: None of these limitations are hard limits. Not every system will have exactly the same limitations, nor will every system encounter these limitations.

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The Effect of Compression and Encryption on Upload Speed

Encryption and compression can have a large effect on upload speed during a Backup to Cloud operation.

If enabled, CSSB has to compress and/or encrypt each block of data before it is uploaded. It takes time to do the compression and/or encryption, and both encryption and compression are CPU-intensive processes. The time it takes to compress and/or encrypt will vary. The power of the CPU, the type of data, and the load on the CPU will all play a part in how long it takes to compress and/or encrypt data. It is possible for compression and/or encryption of a block of data to take longer than uploading that block of data - especially on older machines.

In other words, it is possible that CSSB can upload a block of data so fast that the next block of data isn't ready yet. Although CSSB compresses/encrypts several blocks of data at a time, this delay can bring average transfer speeds down.

It still takes time to compress/encrypt the data during a Backup to Disk and Cloud. However, this is done during the backup to disk phase. Once the backup to disk is complete, CSSB will upload the resulting archive to the cloud at full speed as there will not be any more blocks of data waiting to be compressed or encrypted. 

General Stability During Large Long-Running Backups

CSSB uses Volume Shadow Copy (VSS) snapshots to perform backups. Your machine must keep the snapshot intact during the entire duration of your backup.

During a Backup to Cloud operation, the snapshot must be active and intact for the entire duration of the backup. This can be a very long time, especially for large backups on a slow connection. While a snapshot is active, it must account for all data written to the disk. The more data is written, the larger the snapshot grows. Snapshots are allocated a limited amount of space by Windows. If a snapshot grows larger than this allocated space, it breaks and the backup fails.

Backups to Cloud keep the snapshot open for a long time, long enough that even a light load on the machine can cause the snapshot to break. A machine under a heavy load will cause the snapshot to break faster.

In general, this means that Backups to Disk and Cloud are more stable overall than a Backup to Cloud only, especially for large, long-running operations. For more details on this behavior, please review the Knowledgebase article: Direct Backups to Cloud Fail.

Note: If a backup has not completed before the next backup is scheduled to begin, the new backup will fail, reporting that a backup is already in progress.
Recovering from Network Outages

While a Backup to Cloud can be paused and resumed, it cannot recover from complete failure. Nor can a Backup to Disk be recovered if it fails. If a snapshot fails for any reason, the backup must be restarted.

The upload portion of a Backup to Disk and Cloud can be resumed, even if it fails. The backup has already completed and resides on the local disk. CSSB tracks what has been uploaded, and can just pick up where it left off. CSSB will even try to automatically upload the data to the cloud, as seen in How Does CSSB Handle the Loss of Network Connectivity to the Cloud.

With a Backup to Cloud, the backup and upload processes are linked. If either fails, the backup will fail and cannot be resumed, necessitating that the operation be restarted from the beginning.

Backups to Cloud are viable in most situations on most machines, but the limitations above are real and should not be discounted.

A Backup to Disk and Cloud is the recommended backup type. It is faster, more stable, and recovers from errors better than a Backup to Cloud only. If you suspect there is any chance of encountering one of the limitations mentioned in this article, try a Backup to Disk and Cloud.

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