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Netbackup 7.5 Accelerator and Client-side Deduplication

RLeon
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Hi all,


I've gone through the parts about Accelerator in the 7.5 Admin guide.
I've read though the 7.5 Deduplication guide.
I've read the "Netbackup Accelerator Feature Briefing" document that is only accessible in the seclusive Symantec IQ for Partners portal.

I understand that:
"NetBackup Accelerator should be regarded as a complimentary technology of client deduplication, not replacement for it".

From what I gathered, there doesn't seem to be any disadvantage to using Accelerator.
It almost seems like there is no reason not to enable it, when client-side deduplication is already in use.

My 1st question:
Are there situations in which Accelerator should NOT be enabled when doing client-side deduplication?

I know that Accelerator only supports two policy types, "MS-Windows" and "Standard";
if you disable Accelerator, you could still use client-side deduplication with other policy types such as "Flashbackup".

But apart from that, is there a reason not to use Accelerator when using client-side deduplication?


2nd question:
To force client-side deduplication, the following would have to be set for a client:
  Host Properties > Master Servers > Client Attribute > Always use client-side deduplication

What about if I enable Accelerator in the policy attributes WITHOUT setting the above?
Seeing that Accelerator is based on (or works with) Client-side deduplication, what would happen if I don't specify "Always use client-side deduplication"? would Accelerator still work as it is supposed to? Worst still, what if I mistakenly set "Always use the media server for deduplication" for the client?

If Accelerator would still work, then that means by simplying enabling Accelerator in a policy, the "Always use client-side deduplication" attribute is automatically forced on all the clients in the policy.
If it wouldn't work, then the guides should have mentioned that you have to set "Always use client-side deduplication" for clients inside an Accelerator enabled policy.

Thanks all,

RLeon

1 ACCEPTED SOLUTION

Accepted Solutions

AbdulRasheed
Level 6
Employee Accredited Certified

 

Hi RLeon et al,

    Sorry to be late in this party. You guys have a great discussion going here. In the interest of saving time for someone newly following this thread, I tried to consolidate the questions and provide answers in this blog . Some of these might be obvious to most of you and some of them might have already been answered, I am listing them just to give a full perspective. 

  As Jed already mentioned, if you have a specific issue with growing track log, please do work with technical support. 

 

 

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19 REPLIES 19

revarooo
Level 6
Employee

From memory, no you don't have to set client side deduplication, you can just do normal backup with Accelerator enabled. You MUST be sending the data to a storage unit that supports Accelerator (Dedup, Puredisk, Cloud)

RLeon
Moderator
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Thanks for your input revaroo.

I understand the storage unit prerequisites for using Accelerator.

What you are saying validates my hypothesis:
"... by simplying enabling Accelerator in a policy, the "Always use client-side deduplication" attribute is automatically forced on all the clients in the policy."

That means even if the client normally uses media server deduplication, it will be forced to start using client-side deduplication when you enable Accelerator in the policy.

So then, what if I mistakenly set "Always use the media server for deduplication" for the client? Would Accelerator still work?

Also, can you point me to some answers for my 1st question?

Thanks,

RLeon

Peter_Jakobs
Level 5
Partner Accredited Certified

If you are low on disk space on the client side you can have a problem with the accelerator. I've seen clients with a tracking file of several GB, (and I've seen clients with a disk full thanks to the tracking file)

 

Peter

marcelg
Level 3

I wonder what uses less space - the tracking file or the NTFS Change Journal

RLeon
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I must say I wasn't expecting to see a (potential) fault for being a reason NOT to use Accelerator. But this is useful information, so thanks Peter Jakobs.
I hope they talk more about this tracking file growth problem in the guides.

I was actually expecting to see something along the lines of:

"...under such and such conditions, enabling Accelerator would result in lower bandwidth/cpu/storage resource utilization and the backup becomes less efficient.
But in all other cases, always use Accelerator when using Client-side deduplication..."

...or somesuch.

Thanks,

RLeon
 

marcelg
Level 3

Accelerator and Client-side deduplication are two independent but potentially complementary product features as far as I know.

The customer should always be allowed to choose whether to enable client-side deduplication because of the potentially negative impact on client performance during backups.

RLeon
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Just found another quirk about Accelerator that isn't documented (Ok, I agree this one is a little obvious anyway...):

If you enable Accelerator in a policy's attribute tab, the "compression" and "encryption" check boxes will be disabled.

But then when you think about it, it doesn't really matter, because if you use Accelerator, you are using deduplication anyway.

And as we all know, when using deduplication you cannot use the policy attributes's "compression" and "encryption" options. You have to use the deduplication engine's very own comperssion and encryption features.

RLeon

RLeon
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Anyone with any design considerations and best practices on when and when not to enable Accelerator for client-side deduplication backups?

RLeon
Moderator
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Anyone from Symantec wants to add anything to this?

It is going to be difficult when more and more customers ask the same question...

vholmes
Level 3

I guess the only thing that really bothers me...

If you enable Accelerator, because it also uses Synthetics on the back side, you are unable to create synthetic backups.  For me I do fulls on the weekend, diffs durring the week, but I have to run all the diffs to get a restore to Thursday.  If I just did client side dedup and synthetics the restores would be a little quicker.

Lastly I get random 83s, 14s on some really big file servers.  Maybe I am missing something but that is my experience.

RLeon
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Hi vholmes,

Thanks for keeping this thread alive :)

Good point about not being able to select "Synthetic Backup" in a schedule when Accelerator is enabled; didn't know about that.
As you said, it is probably because Accelerator itself uses it as part of its "Optimized Synthethic Backup" routine.

As for the errors, are you using iScsi connections for your deduplication storage?
This configuration isn't supported until Netbackup 7.5, and even then, only 10Gb iScsi is officially supported for the deduplication storage.

RLeon

 

Marianne
Moderator
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Partner    VIP    Accredited Certified

Accelerator IS optimized Synthetic Backup.

What I find worrying is the large track/journal log on the client with apparently no solution (yet).

See this discussion: https://www-secure.symantec.com/connect/forums/accelerator-caused-journal-log-80-gb

 

RLeon
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So apparently the large track log problem is still present in 7.5.0.3... Interesting.

As I have said earlier in this thread, although this is a reason to NOT use Accelerator, this is not an official reason.
I'm still waiting for the official word - from a kind of Best Practice perspective - that in what situations Accelerator should not be used together with Client Side Deduplicatoin.

Note that I'm not referring to situations where Accelerator could not be used;
such as when you want to manually use the traditional Synthetic Backups (non-Optimized),
or when you simply do not have a deduplication storage unit,
or when you want to use other policy types such as flashbackup,
etc.

I'm referring to situations where Accelerator could be enabled, but should not.
Any if such situations exist, I would like to know the reason.

RLeon

Jed_Gresham
Level 4
Employee Accredited

Accelerator does not require source dedupe or force it on when enabled.  You can still dedupe on the media server instead of at the client when you use accelerator.

 

When you run the backup does the track log clear out or does it remain very large?  

 

One of the things we'll have to get used to with accelerator is the paradigm shift it may be causing.  What you might want to try is scheduling backups to run more often on these servers where the track log is filling up because of a high change rate.  You can setup backups for every 4 hours that expire after 24 or 48, and then keep your normal daily backups at the retention you currently have.  Might be worth a test if nothing else.  Could also give you some pretty good RPO.

RLeon
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Hi Jed,

Thank you for your input.

I understand how Accelerator could be used together with client-side deduplication, and that they do not necessarily have to be used together.
It is also clear that when Accelerator is enabled, it does not force client-side deduplication. (Like what I was suggesting previously; which was wrong.)

You are suggesting that if data change rate is high, then the track log could be large. That makes technical sense.
You also suggested that this problem could be remedied by running backups more often. That is fair enough.
(Even though apparently the track log is only supposed to be around 30MB according to the thread linked to by Marianne)

Can you also shed some light on my query from the post that is directly above yours? That one about when-not-to-use Accelerator.

I understand that Accelerator is not really for clients with a very high change rate, and I consider that a valid reason for not using Accelerator.
But then, the same reason also applies to deduplication backups without Accelerator (client or server side).
Actually, one could argue that it also applies to the traditional file level incremental backups: The higher the change rate, the less useful the incremental backup method becomes.

In short, while a valid reason, the high-change-rate-makes-it-less-useful reasoning is not unique to Accelerator.
I know I've repeated this many times already, but is there a reason, unique to Accelerator, that one should not use it even when it could be used?

Thanks,

RLeon

Jed_Gresham
Level 4
Employee Accredited

A few things: 

  • Although there are real reasons for the track log to get larger than normal, the size cited is unusual and should be investigated by support.  
  • Normal is relative and dependent on the number of files on the file system.  
  • Change rate in this case means how many files have changed since the last backup, not how much raw data has been churned.

To answer your question about when not to use accelerator.  I would say there are less times to describe when accelerator is not good and more to describe when something else is better.  

  • Hugely overburdened file systems that are highly fragmented with millions and millions of files... that's still probably a pretty good time to use flashbackup instead of accelerator.  Accelerator is not intended to be a repalcement for this functionality.
  • Backing up a VM... I'd still use VADP integration (for the most part) rather than an agent with accelerator backups inside the VM. 

That's a couple of examples.  Do you get my point though?

Jed_Gresham
Level 4
Employee Accredited

Also, let me correct my previous statement.  The track log is a function of the number of files and should only significantly change when the number of files on the file system significantly changes.  Apologies for the incorrect info.

Anyone who has a track log growing to the size mentioned in some of these posts (80gb, etc) should contact support and have them investigate.

AbdulRasheed
Level 6
Employee Accredited Certified

 

Hi RLeon et al,

    Sorry to be late in this party. You guys have a great discussion going here. In the interest of saving time for someone newly following this thread, I tried to consolidate the questions and provide answers in this blog . Some of these might be obvious to most of you and some of them might have already been answered, I am listing them just to give a full perspective. 

  As Jed already mentioned, if you have a specific issue with growing track log, please do work with technical support. 

 

 

RLeon
Moderator
Moderator
   VIP   

Jed and Abdul,

Thank you both for jumping in with the new info.

From the blog:

Are there any design considerations when not to use NetBackup Accelerator when NetBackup Client Side Deduplication is used?
No! NetBackup Accelerator does not have any negative effects on NetBackup Client Side Deduplication.

I like that exclamation mark, a lot.
I can get some sleep now.

Thanks all!

RLeon