Basics – Cloning vs Staging

 Basics, NetWorker  No Responses »
Mar 212011
 

When people are just starting to get into NetWorker, a common situation is that they get confused about the difference between cloning and staging. (This isn’t helped given NetWorker can report in-progress staging operations as cloning – a perennial source of annoyment.)

So, what’s the difference?

  • A clone operation is where NetWorker duplicates a saveset. It makes a registered copy of the saveset, and at the conclusion of the operation is aware that it has an additional copy.
  • A stage operation is where NetWorker moves a saveset. It first makes a registered copy of the saveset, and then at the conclusion of the operation removes reference to the instance that it copied from.

Typically when we talk about staging, we talk about moving from a disk (media type ‘FILE’ or media type ‘ADV_FILE’) volume to tape. In such a situation where NetWorker stages from an actual FILE/ADV_FILE volume, it not only removes reference to the original saveset, but it actually removes it from the source volume as well. That’s to be expected – it’s a real disk filesystem that NetWorker is accessing, and removing a saveset is as simple as just running an operating system ‘delete’ command.

While it’s not often done, NetWorker does support staging from tape – but obviously when it’s done reading from the source volume, it can’t then selectively erase chunks of savesets from the source tape. Instead, all it does in that situation is delete, from the media database, the reference to the saveset having been on the source volume.

(In case you’re new to NetWorker and intend to now run off and try some staging – make sure, please, before you do, to read the second article ever posted on the NetWorker Blog – “Instantiating Savesets“. It has some very cautionary information about staging operations.)

One final thing – while I said that a clone or stage operation is done against a saveset, it’s not always as simple as that. If you tell NetWorker to clone or stage an individual saveset/saveset instance, that’s exactly what it will do. However, if you tell NetWorker to clone or stage a NetWorker tape volume, it will clone/stage the entire volume, with multiplexing left intact.

Regardless of those caveats though, remember the simple rule – a clone is a copy operation, and a stage is a move operation.

 Posted by at 05:49  Tagged with: , , , , ,

ADV_FILE devices and tape rotation strategies

 Architecture, NetWorker, Policies, Scripting  3 Responses »
Mar 032010
 

While I touched on this in the second blog posting I made (Instantiating Savesets), it’s worthwhile revisiting this topic more directly.

Using ADV_FILE devices can play havoc with conventional tape rotation strategies; if you aren’t aware of these implications, it could cause operational challenges when it comes time to do recovery from tape. Let’s look at the lifecycle of a saveset in a disk backup environment where a conventional setup is used. It typically runs like this:

  1. Backup to disk
  2. Clone to tape
  3. (Later) Stage to tape
  4. (At rest) 2 copies on tape

    Looking at each stage of this, we have:

    Saveset on ADV_FILE deviceThe saveset, once written to an ADV_FILE volume, has two instances. The instance recorded as being on the read-read only part of the volume will have an SSID/CloneID of X/Y. The instance recorded as being on the read-write part of the volume will have an SSID/CloneID of X/Y+1. This higher CloneID is what causes NetWorker, upon a recovery request, to seek the “instance” on the read-only volume. Of course, there’s only one actual instance (hence why I object so strongly to the ‘validcopies’ field introduced in 7.6 reporting 2) – the two instances reported are “smoke and mirrors” to allow simultaneous backup to and recovery from an ADV_FILE volume.

    The next stage sees the saveset cloned:

    ADV_FILE + Tape CloneThis leaves us with 3 ‘instances’ – 2 physical, one virtual. Our SSID/CloneIDs are:

    • ADV_FILE read-only: X/Y
    • ADV_FILE read-write: X/Y+1
    • Tape: X/Y+n, where n > 1.

    At this point, any recovery request will still call for the instance on the read-only part of the ADV_FILE volume, so as to help ensure the fastest recovery initiation.

    At some future point, as disk capacity starts to run out on the ADV_FILE device, the saveset will typically be staged out:

    ADV_FILE staging to tapeAt the conclusion of the staging operation, the physical + virtual instances of the saveset on the ADV_FILE device are removed, leaving us with:

    Savesets on tape only

    So, at this point, we end up with:

    • A saveset instance on a clone volume with SSID/CloneID of: X/Y+n.
    • A saveset instance on (typically) a non-clone volume with SSID/CloneID of: X/Y+n+m, where m > 0.

    So, where does this leave us? (Or if you’re not sure where I’ve been heading yet, you may be wondering what point I’m actually trying to make.)

    Note what I’ve been saying each time – NetWorker, when it needs to read from a saveset for recovery purposes, will want to pick the saveset instance with the lowest CloneID. At the point where we’ve got a clone copy and a staged copy, both on tape, the clone copy will have the lowest CloneID.

    The net result is that NetWorker will, in these circumstances, when both tapes aren’t online, request the clone volume for recovery – even though in an extreme number of cases, this will be the volume that’s offsite.

    For NetWorker versions 7.3.1 and lower, there was only one solution to this – you had to hunt down the actual clone saveset instances NetWorker was asking for, mark them as suspect, and reattempt the recovery. If you managed to mark them all as suspect, then you’d be able to ‘force’ NetWorker into facilitating the recovery from the volume(s) that had been staged to. However, after the recovery you had to make sure you backed out of those changes, so that both the clones and the staged copies would be considered not-suspect.

    Some companies, in this situation, would instigate a tape rotation policy such that clone volumes would be brought back from off-site before savesets were likely to be staged out, with subsequently staged media sent offsite. This has a dangerous side-effect of temporarily leaving all copies of backups on-site, jeapordising disaster recovery situations, and hence it’s something that I couldn’t in any way recommend.

    The solution introduced around 7.3.2 however is far simpler – a mminfo flag called offsite. This isn’t to be confused with the convention of setting a volume location field to ‘offsite’ when the media is removed from site. Annoyingly, this remains unqueryable; you can set it, and NetWorker will use it, but you can’t say, search for volumes with the ‘offsite’ flag set.

    The offsite flag has to be manually set, using the command:

    # nsrmm -o offsite volumeName

    (where volumeName typically equals the barcode).

    Once this is set, then NetWorker’s standard saveset (and therefore volume) selection criteria is subtly adjusted. Normally if there are no online instances of a saveset, NetWorker will request the saveset with the lowest CloneID. However, saveset instances that are on volumes with the offsite flag set will be deemed ineligible and NetWorker will look for a saveset instance that isn’t flagged as being offsite.

    The net result is that when following a traditional backup model with ADV_FILE disk backup (backup to disk, clone to tape, stage to tape), it’s very important that tape offsiting procedures be adjusted to set the offsite flag on clone volumes as they’re removed from the system.

    The good news is that you don’t normally have to do anything when it’s time to pull the tape back onsite. The flag is automatically cleared* for a volume as soon as it’s put back into an autochanger and detected by NetWorker. So when the media is recycled, the flag will be cleared.

    If you come from a long-term NetWorker site and the convention is still to mark savesets as suspect in this sort of recovery scenario, I’d suggest that you update your tape rotation policies to instead use the offsite flag. If on the other hand, you’re about to implement an ADV_FILE based backup to disk policy, I’d strongly recommend you plan in advance to configure a tape rotation policy that uses the offsite flag as cloned media is sent away from the primary site.

    –
    * If you did need to explicitly clear the flag, you can run:

    # nsrmm -o notoffsite volumeName

    Which would turn the flag back off for the given volumeName.

     Posted by at 09:37  Tagged with: , , , , ,

    Basics – Need a different volume from pool …

     Basics, NetWorker  3 Responses »
    Feb 222010
     

    The scenario:

    • A clone or stage operation has aborted (or otherwise failed)
    • It has been restarted
    • It hangs waiting for a new volume even though there’s a partially written volume available.

    This is a relatively easy problem to explain. Let’s first look at the log messages that happens. To generate this error, I started cloning some data to the “Default Clone” pool, with only one volume in the pool, then aborted. Shortly thereafter I tried to run the clone again, and when NetWorker wouldn’t write to the volume I unmounted and remounted it – a common thing that newer administrators will try in this scenario. This is where you’ll hit the following error in the logs:

    media notice: Volume `800829L4' ineligible for this operation; Need a different volume
from pool `Default Clone'
media info: Suggest manually labeling a new writable volume for pool 'Default Clone'

    So, what’s the cause of this problem? It’s actually relatively easy to explain.

    A core component in NetWorker’s media database design is that a saveset can only ever have one instance on a piece of media. This applies as equally to failed as complete saveset instances.

    The net result is that this error/situation will occur because it’s meant to – NetWorker doesn’t permit more than one instance of a saveset to appear on the same piece of physical media.

    So what do you do when this error comes up?

    • If you’re backing up to disk, an aborted saveset should normally be cleared up automatically by NetWorker after the operation is aborted. However, in certain instances this may not be the case. For NetWorker 7.5 vanilla and 7.5.1.1/7.5.1.2, this should be done by expiring the saveset instance – using nsrmm to flag the instance as having an expiry date within a few minutes or seconds. For all other versions of NetWorker, you should just be able to delete the saveset instance.
    • When working with tape (virtual or physical), the most recommended approach would be to move on to another tape, or if the instance is the only instance on that tape, relabel the tape. (Some would argue that you can use nsrmm to delete the saveset instance from the tape and then re-attempt the operation, but since NetWorker is so heavily designed to prevent multiple instances of a saveset on a piece of media, I’d strongly recommend against this.)

    Overall it’s a fairly simple issue, but knowing how to recognise it lets you resolve it quickly and painlessly.

     Posted by at 19:40  Tagged with: , , , , , , , , ,

    The top 10 for 2009

     Architecture, Basics, NetWorker, Quibbles, Site, Support  No Responses »
    Jan 062010
     

    Looking at the stats both for this new site and the previous site, I’ve compiled a list of the top 10 read articles on The NetWorker Blog for 2009. The top 3 of course match the three articles that routinely turn out to be the most popular on any given month, which speaks something of their relevance to the average NetWorker administrator.

    (Note: I’ve excluded non-article pages from the top 10.)

    Number 10 – Instantiating Savesets

    The very first article on the blog, Instantiating Savesets detailed the importance of distinguishing between all instances of a saveset and a specific instance of a saveset.

    This distinction between using just the saveset ID, and using a saveset ID/clone ID combination becomes particularly important when staging from disk backup units. If clones exist and you stage using just the saveset ID, when NetWorker cleans up at the end of the staging operation it will remove reference to the clones as well as deleting the original from the disk backup unit. (Something you really don’t want to have happen.)

    Recommendation to EMC: Perhaps it would be worthwhile requiring a “-y” argument to nsrstage if staging savesets from disk backup units and specifying only the saveset ID.

    Recommendation to NetWorker administrators: Always be careful when staging that you specify both the saveset and the clone ID.

    Number 9 – Basics – Important mminfo fields

    In May I wrote about a few key mminfo fields – notably:

    • savetime
    • sscreate
    • ssinsert
    • sscomp
    • ssaccess

    Sadly, I didn’t get the result I wanted with EMC on ssaccess. Documented as being updated whenever a saveset fragment is accessed for backup and recovery, the most I could get was an acknowledgement that it was currently broken and to lodge an RFE to get it fixed. (The alternative was to have the documentation changed to take out reference to read operations – something I didn’t want to have happen!)

    Recommendation to EMC: ssaccess would be a particularly useful mminfo field, particularly when analysing recovery statistics for NetWorker. Please fix it.

    Number 8 – Basics – Listing files in a backup

    Want to know what files were backed up as part of the creation of a saveset? If you do, you’re not unique – this has remained a very popular article since it was written in January.

    Recommendation to EMC: This information can be retrieved via a combination of mminfo/nsrinfo, but it would be handy if NMC supported drilling down into a saveset to provide a file listing.

    Number 7 – Using yum to install NetWorker on Linux

    NetWorker’s need for dependency resolution on Linux for installation of the client packages in particular drew a lot of people to this article.

    Number 6 – Basics – mminfo, savetime, and greater than/less than

    This article explained why NetWorker uses the greater than and less than signs in mminfo in a way that newcomers to the product might find backwards. If you’re not aware of why mminfo works the way it does for specifying savetimes, you should be.

    Number 5 – 7.5(.1) changed behaviour – deleting savesets from adv_file devices

    This was a particularly unpleasant bug introduced into NetWorker 7.5, thankfully resolved now in the cumulative service releases and NetWorker 7.6

    The gist of it is that in NetWorker 7.5/7.5.1 (aka 7.5 SP1), if you deleted a saveset on a disk backup unit, NetWorker would suffer a serious failure where it would from that point have issues cleaning regular expired savesets from the disk backup unit and insist that the disk backup unit had major issues. The primary error would manifest as:

    nsrd adv_file warning: Failed to fetch the saveset(ss_t) structure for ssid 1890993582

    This was fixed in 7.5.1.2, thankfully.

    Recommendation to EMC: Never let this bug see the light of day again, please. (So far you’re doing an excellent job, by the way.)

    Number 4 – NetWorker 7.5.1 Released

    I’ve recently noticed a disturbing trend among many vendors, EMC included, where once a new release is made of a product, sales and account staff become overly enthusiastic about recommending new releases. This comes on top of not really having any technical expertise. (Please be patient, I’m trying to put this as diplomatically as possible.)

    One of the worst instances I’ve seen of this in the last few years was the near-hysterical pumping of 7.5 thanks to some useful features to do with virtualisation in particular. I’ll admit that my articles on the integration between Oracle Module 5 and NetWorker 7.5, as well as Probe Based Backups may have added to this. However, there was somewhat of a stampede to 7.5 when it came out, and consequently, when it had some issues, there was strong enthusiasm for the release of 7.5.1.

    This is why, by the way, that IDATA maintains for its support customers a recommended versions list that is not automatically updated when new versions of products come out.

    Recommendation to EMC: Remind your sales staff that existing users already have the product, and not to just go blindly convincing them to upgrade. Otherwise you’ll eventually start sounding like this.

    Number 3 – Carry a jukebox with you (if you’re using Linux)

    During 2009, Mark Harvey’s LinuxVTL project first got the open source LinuxVTL working with NetWorker in a single drive configuration, then eventually, in multi-drive configurations. (Mark assures me, by the way, that patches are coming real soon to allow multiple robots on the same storage node/server.)

    Lesson for me: With the LinuxVTL configured on multiple lab servers in my environment, I’ve really taken to VTLs this year, and considerably changed my attitude on using them. (I’ll say again: I still resent that they’re needed, but I now respect them a lot more than I previously did.)

    Lesson for others: Even Mark himself says that the open source VTL shouldn’t be used for production backups. Don’t be cheap with your backup system, this is an excellent tool for lab setups, training, diagnostics, etc., but it is not a replacement to a production-ready VTL system. If you want a VTL, buy a VTL.

    Number 2 – Basics – Parallelism in NetWorker

    Some would say that the high popularity of an article about parallelism in NetWorker indicates that it’s not sufficiently documented.

    I’m not entirely convinced that’s the case. But it does go to show that it’s an important topic when it comes to performance tuning, and summary articles about how the various types of parallelism interact are obviously popular.

    Lesson for everyone: Now that the performance tuning guide has been updated and made more relevant in NetWorker 7.6, I’d recommend people wanting an official overview of some of the parallelism options checking that out in addition to the article above.

    Number 1 – Basics – Fixing “NSR peer information” errors

    Goodness this was a popular article in 2009 – detailing how to fix the “NSR peer information” errors that can come up from time to time in the NetWorker logs. If you’re not familiar with this error yet, it’s likely you will eventually as a NetWorker administrator see an error such as:

    39078 02/02/2009 09:45:13 PM  0 0 2 1152952640 5095 0 nox nsrexecd SYSTEM error: There is already a machine using the name: “faero”. Either choose a different name for your machine, or delete the “NSR peer information” entry for “faero” on host: “nox”

    Recommendation for EMC: Users shouldn’t really need to be Googling for a solution to this problem. Let’s see an update to NetWorker Management Console where these errors/warnings are reported in the monitoring log, with the administrator being able to right click on them and choose to clear the peer information after confirming that they’re confident no nefarious activity is happening.

    Wrapping Up

    I have to say, it was a fantastically satisfying year writing the blog, and I’m looking forward to seeing what 2010 brings in terms of most useful articles.

     Posted by at 06:41  Tagged with: , , , , , , , , , , , , , , , , , , , , , , , ,

    Manually Staging? Don’t forget the Clone ID!

     Basics, NetWorker, Scripting  5 Responses »
    Nov 132009
     

    Something that continues to periodically come up is the need to remind people running manual staging to ensure they specify both the SSID and the Clone ID when they stage. I did some initial coverage of this when I first started the blog, but I wanted to revisit and demonstrate exactly why this is necessary.

    The short version of why is simple: If you stage by SSID alone, NetWorker will delete/purge all instances of the saveset other than the one you just created. This is Not A Good Thing for 99.999% of what we do within NetWorker.

    So to demonstrate, here’s a session where I:

    1. Generate a backup
    2. Clone the backup to tape
    3. Stage the saveset only to tape

    In between each step, I’ll run mminfo to get a dump of what the media database says about saveset availability.

    Part 1 – Generate the Backup

    Here’s a very simple backup for the purposes of this demonstration, and the subsequent mminfo command to find out about the backup:

    [root@tara ~]# save -b Default -LL -q /etc
save: /etc  106 MB 00:00:07   2122 files
completed savetime=1258093549

[root@tara ~]# mminfo -q "client=tara.pmdg.lab,name=/etc" -r volume,ssid,cloneid,
savetime
 volume        ssid          clone id  date
Default.001    2600270829  1258093549 11/13/2009
Default.001.RO 2600270829  1258093548 11/13/2009

    There’s nothing out of the ordinary here, so we’ll move onto the next step.

    Part 2 – Clone the Backup

    We’ll just do a manual clone to the Default Clone pool. Here we’ll specify the saveset ID alone, which is fine for cloning – but is often what leads people to being in the habit of not specifying a particular saveset instance. I’m using very small VTL tapes, so don’t be worried that in this case I’ve got a clone of /etc spanning 3 volumes:

    [root@tara ~]# nsrclone -b "Default Clone" -S 2600270829
[root@tara ~]# mminfo -q "client=tara.pmdg.lab,name=/etc" -r volume,ssid,cloneid,
savetime
 volume        ssid          clone id  date
800843S3       2600270829  1258094164 11/13/2009
800844S3       2600270829  1258094164 11/13/2009
800845S3       2600270829  1258094164 11/13/2009
Default.001    2600270829  1258093549 11/13/2009
Default.001.RO 2600270829  1258093548 11/13/2009

    As you can see there, it’s all looking fairly ordinary at this point – nothing surprising is going on at all.

    Part 3 – Stage by Saveset ID Only

    In this next step, I’m going to stage by saveset ID alone rather than specifying the saveset ID/clone ID, which is the correct way of staging, so as to demonstrate what happens at the conclusion of the staging. I’ll be staging to a pool called “Big”:

    [root@tara ~]# nsrstage -b Big -v -m -S 2600270829
Obtaining media database information on server tara.pmdg.lab
Parsing save set id(s)
Migrating the following save sets (ids):
 2600270829
5874:nsrstage: Automatically copying save sets(s) to other volume(s)

Starting migration operation...
Nov 13 17:34:00 tara logger: NetWorker media: (waiting) Waiting for 1 writable
volume(s) to backup pool 'Big' disk(s) or tape(s) on tara.pmdg.lab
5884:nsrstage: Successfully cloned all requested save sets
5886:nsrstage: Clones were written to the following volume(s):
 BIG991S3
6359:nsrstage: Deleting the successfully cloned save set 2600270829
Successfully deleted original clone 1258093548 of save set 2600270829
from media database.
Successfully deleted AFTD's companion clone 1258093549 of save set 2600270829
from media database with 0 retries.
Successfully deleted original clone 1258094164 of save set 2600270829
from media database.
Recovering space from volume 4294740163 failed with the error
'Cannot access volume 800844S3, please mount the volume or verify its label.'.
Refer to the NetWorker log for details.
6330:nsrstage: Cannot access volume 800844S3, please mount the volume
or verify its label.
Completed recover space operation for volume 4177299774
Refer to the NetWorker log for any failures.
Recovering space from volume 4277962971 failed with the error
'Cannot access volume 800845S3, please mount the volume or verify its label.'.
Refer to the NetWorker log for details.
6330:nsrstage: Cannot access volume 800845S3, please mount the volume
or verify its label.
Recovering space from volume 16550059 failed with the error
'Cannot access volume 800843S3, please mount the volume or verify its label.'.
Refer to the NetWorker log for details.
6330:nsrstage: Cannot access volume 800843S3, please mount the volume
or verify its label.

    You’ll note there’s a bunch of output there about being unable to access the clone volumes the saveset was previously cloned to. When we then check mminfo, we see the consequences of the staging operation though:

    [root@tara ~]# mminfo -q "client=tara.pmdg.lab,name=/etc" -r volume,ssid,cloneid,
savetime
 volume        ssid          clone id  date
BIG991S3       2600270829  1258095244 11/13/2009

    As you can see – no reference to the clone volumes at all!

    Now, has the clone data been erased? No, but it has been removed from the media database, meaning you’d have to manually scan the volumes back in order to be able to use them again. Worse, if those volumes only contained clone data that was subsequently removed from the media database, they may become eligible for recycling and get re-used before you notice what has gone wrong!

    Wrapping Up

    Hopefully the above session will have demonstrated the danger of staging by saveset ID alone. If instead of staging by saveset ID we staged by saveset ID and clone ID, we’d have had a much more desirable outcome. Here’s a (short) example of that:

    [root@tara ~]# save -b Default -LL -q /tmp
save: /tmp  2352 KB 00:00:01     67 files
completed savetime=1258094378
[root@tara ~]# mminfo -q "name=/tmp" -r volume,ssid,cloneid
 volume        ssid          clone id
Default.001    2583494442  1258094378
Default.001.RO 2583494442  1258094377
[root@tara ~]# nsrclone -b "Default Clone" -S 2583494442

[root@tara ~]# mminfo -q "name=/tmp" -r volume,ssid,cloneid
 volume        ssid          clone id
800845S3       2583494442  1258095244
Default.001    2583494442  1258094378
Default.001.RO 2583494442  1258094377
[root@tara ~]# nsrstage -b Big -v -m -S 2583494442/1258094377
Obtaining media database information on server tara.pmdg.lab
Parsing save set id(s)
Migrating the following save sets (ids):
 2583494442
5874:nsrstage: Automatically copying save sets(s) to other volume(s)

Starting migration operation...

5886:nsrstage: Clones were written to the following volume(s):
 BIG991S3
6359:nsrstage: Deleting the successfully cloned save set 2583494442
Successfully deleted original clone 1258094377 of save set 2583494442 from
media database.
Successfully deleted AFTD's companion clone 1258094378 of save set 2583494442
from media database with 0 retries.
Completed recover space operation for volume 4177299774
Refer to the NetWorker log for any failures.

[root@tara ~]# mminfo -q "name=/tmp" -r volume,ssid,cloneid
 volume        ssid          clone id
800845S3       2583494442  1258095244
BIG991S3       2583494442  1258096324

    The recommendation that I always make is that you forget about using saveset IDs alone unless you absolutely have to. Instead, get yourself into the habit of always specifying a particular instance of a saveset ID via the “ssid/cloneid” option. That way, if you do any manual staging, you won’t wipe out access to data!

     Posted by at 16:45  Tagged with: , , , , ,

    Quibbles – Cloning and Staging

     Quibbles  No Responses »
    Aug 132009
     

    For the most part cloning and staging within NetWorker are pretty satisfactory, particularly when viewed from a combination of automated and manual operations. However, one thing that constantly drives me nuts is the inane reporting of status for cloning and staging.

    Honestly, how hard can it be to design cloning and staging to accurately report the following at all times:

    Cloning X of Y savesets, W GB of Z GB

    or

    Staging X of Y savesets, W GB of Z GB

    While there have been various updates to cloning and staging reporting, and sometimes it at least updates how many savesets it has done, it continually breaks when dealing with the total amount staged/cloned in as much as it resets whenever a destination volume is changed.

    Oh, and while I’m begging for this change, I will request one other – include in daemon.raw whenever cloning/staging occurs, the full list of ssid/cloneids that have been cloned or staged, and the client/saveset details for each one – not just minimal details when a failure occurs. It’s called auditing.

     Posted by at 07:21  Tagged with: , , , ,
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