does NO_CHECKSUM makes any difference in backup SIZE

Hi Experts,

Though WITH_CHECKSUM" option is suggested while doing the backups, but if using  "NO_CHECKSUM" makes any difference in backup SIZE. Please share with thoughts.

September 3rd, 2015 5:41am

Why not testing it?

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September 3rd, 2015 5:54am

Hi Experts,

Though WITH_CHECKSUM" option is suggested while doing the backups, but if using  "NO_CHECKSUM" makes any difference in backup SIZE. Please share with thoughts.

No checksup only checks pages when they are backed up or when they are read from disk into memory. The consistency check is limited. Apart from that I am not aware it does any more task. This would not add any data whatsoever so NO it is not going to affect the backup
September 3rd, 2015 6:49am

No, it does not affect a size of the backup

/*

When the WITH CHECKSUM option is used for a backup, the backup process will test the page checksums that exist on the data file pages being backed up. If a bad page checksum is found, the backup process will stop (by default you can override this using WITH CONTINUE_AFTER_ERROR but Id only do that in an emergency). So if the backup completes successfully, you know that there are no broken page checksums.

*/

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September 3rd, 2015 6:55am

Dear Stefan

Thanks for your reply.

I actually checked the backup of two databases with both options [with checksum and with no_checksum(defualt)] but found exactly the same size of the backups. (size of backups was over 1GB)

As the following doc says

https://msdn.microsoft.com/en-us/library/ms186865.aspx

CHECKSUM

Specifies that the backup operation will verify each page for checksum and torn page, if enabled and available, and generate a checksum for the entire backup.

does this checksum information is the part of backup itself, if yes, it is so tiny that it will not impact the size? This raises the question which I put here in the forum.

regards

khalil



September 3rd, 2015 7:14am

does this checksum information is the part of backup itself, if yes, it is so tiny that it will not impact the size? This raises the question which I put here in the forum.

When you enable backup with checksum option all pages which wuld read from disk for backup would be checked and this is what BOL doc says. Yes checksum is part of backup and would only be considered with this backup.

Again it just checks consistency of page read from disk this is all it does.

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September 3rd, 2015 8:37am

Hi Experts,

Though WITH_CHECKSUM" option is suggested while doing the backups, but if using  "NO_CHECKSUM" makes any difference in backup SIZE. Please share with thoughts.

No checksum only checks pages when they are backed up or when they are read from disk into memory. The consistency check is limited. Apart from that I am not aware it does any more task. This would not add any data whatsoever so NO it is not going to affect the backup
September 3rd, 2015 10:44am

It doesn't cause any increase in size of your backup but your Backup time. In order to complete the process it takes a bit more time than usual.
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September 3rd, 2015 2:00pm

The text you quoted say that CHECKSUM does *two* things:

1. Check each page checksum, and it will error if it fines any that isn't correct. This is a check and generates nothing that would be stored anywhere.

2. Calculate a checksum over the entire content of the backup. This is written in the header and is indeed so tiny so it doesn't impact backup size.

September 3rd, 2015 3:58pm

The text you quoted say that CHECKSUM does *two* things:

1. Check each page checksum, and it will error if it fines any that isn't correct. This is a check and generates nothing that would be stored anywhere.

2. Calculate a checksum over the entire content of the backup. This is written in the header and is indeed so tiny so it doesn't impact backup

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September 4th, 2015 2:59pm

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