![\"AFTD](\"https:\/\/nsrd.info\/blog\/wp-content\/uploads\/2012\/07\/AFTD-changes-v7.x-AFTD.jpg\" "\\"AFTD")
<\/a><\/p>\n(In the above diagram, and those to follow, a red line\/arrow indicates a write session coming into the AFTD, and a green line\/arrow indicates a read session coming out of the AFTD.)<\/p>\n
That is, you’d slice and dice that theoretical 10TB of disk capacity into a bunch of smaller sized filesystems, with typically one AFTD per filesystem. In 7.x, there are two nsrmmd processes per AFTD \u2013 one to handle write operations (the main\/real path to the AFTD), and one to handle read operations from the AFTD device \u2013 the shadow or _AF_readonly path on the volume.<\/p>\n
So AFTDs under this scenario delivered simultaneous backup and recovery operations by a bit of sleight-of-hand; in some ways, NetWorker was\u00a0tricked<\/em> into thinking it was dealing with two different volumes. In fact, that’s what lead to there being two instances of a saveset in the media database for any saveset created on AFTD \u2013 one for the read\/write volume, and one of the read-only volume, with a clone ID of 1 less than the instance on the read\/write volume. This didn’t double the storage; the “trick” was largely maintained in the media database, with just a few meta files maintained in the _AF_readonly path of the device.<\/p>\n Despite the improved backup options offered by v7.x AFTDs, there were several challenges introduced that somewhat limited the applicability of AFTDs in larger backup scenarios. Much as I’ve never particularly<\/em> liked virtual tape libraries (seeing them as a solution to a problem that shouldn’t exist), I found myself typically recommending a VTL for disk backup in NetWorker ahead of AFTDs. The challenges in particular, as I saw them, were:<\/p>\n As a result of this, a lot of AFTD layouts saw them more being used as glorified staging units, rather than providing a significant amount of near-line recoverability options.<\/p>\n Another, more subtle problem from this architecture was that nsrmmd itself is not a process geared towards a high amount of concurrency; while based on its name (media multiplexor daemon) we know that it’s always been designed to deal with a certain number of concurrent streams for tape based multiplexing, there are limits to how many savesets an nsrmmd process can handle simultaneously before it starts to dip in efficiency. This was never so much an issue with physical tape \u2013 as most administrators would agree, using multiplexing above 4 for any physical tape will continue to work, but may result in backups which are much slower to recover from if a full filesystem\/saveset recovery is required, rather than a small random chunk of data.<\/p>\n NetWorker administrators who have been using AFTD for a while will equally agree that pointing a large number of savesets at an AFTD doesn’t guarantee high performance \u2013 while disk doesn’t shoe-shine, the drop-off in nsrmmd efficiency per saveset would start to be quite noticeable at a saveset concurrency of around 8 if client and network performance were not the bottleneck in the environment.<\/p>\n This further encouraged slicing and dicing disk backup capacity \u2013 why allocate 10TB of capacity to a single AFTD if you’d get better concurrency out of 5 x 2TB AFTDs? To minimise the risk of any individual AFTD filling while others still had capacity, you’d configure the AFTDs to each have target sessions of 1 – effectively round-robbining the \u00a0starting of savesets across all the units.<\/p>\n I think that pretty much provides a good enough overview about AFTDs under v7.x that can talk about AFTDs in NetWorker v8.<\/p>\n Keeping that 10TB of disk backup capacity in play, under NetWorker v8, you’d optimally end up with the following configuration:<\/p>\n You’re seeing that right \u2013 multiple nsrmmd processes for a single AFTD \u2013 and I don’t mean a read\/write nsrmmd and a shadow-volume read-only nsrmmd as per v7.x. In fact, the entire concept and implementation of the shadow volume goes away under NetWorker v8. It’s not needed any longer.\u00a0Huzzah!<\/strong><\/p>\n Assuming dynamic nsrmmd spawning (yes), and up to certain limits, NetWorker will now spawn one nsrmmd process for an AFTD each time it hits the\u00a0target sessions<\/em> setting for the AFTD volume. That raises one immediate change \u2013 for a v8.x AFTD configuration, bump up the target sessions for the devices. Otherwise you’ll end up spawning a lot more nsrmmd processes than are appropriate. Based on feedback from EMC, it would seem that the optimum target setting for a consolidate AFTD is 4. Assuming linear growth, this would mean that you’d have the following spawning rate:<\/p>\n Your actual rate may vary of course, depending on cloning, staging and recovery operations also being performed at the same time. Indeed, for the time being at least, NetWorker dedicates a single nsrmmd process to any\u00a0nsrclone<\/em> or\u00a0nsrstage<\/em> operation that is run (either manually or as a scheduled task), and yes, you can actually simultaneously recover, stage and clone all at the same time. NetWorker handles staging in that equation by blocking capacity reclamation while a process is reading from the AFTD \u2013 this prevents a staging operation removing a saveset that is needed for recovery or cloning. In this situation, a staging operation will report as per:<\/p>\n When a space reclamation is subsequently run (either as part of overnight reclamation, or an explicit execution of nsrim -X), the something along the following lines will get logged:<\/p>\n Thus, you shouldn’t need to worry about concurrency any longer.<\/p>\n Another change introduced to the AFTD architecture is the device name is now divorced from the\u00a0path<\/em>. This is stored in a different field. For example:<\/p>\n In the above example, the AFTD device has a device name of AFTD1, and the path to it is \/d\/backup1 \u2013 or to be more accurate, the\u00a0first<\/em> path to it is \/d\/backup1. I’ll get to the real import of that in a moment.<\/p>\n There is a simpler management benefit: previously if you setup an AFTD and needed to later change the path that it was mounted from, you had to do the following:<\/p>\n This was a tedious process, and the notion of “deleting” an AFTD, even though it had no bearing on the actual data stored on it, did not appeal to a lot of administrators.<\/p>\n However, the first path specified to an AFTD in the “Device Access Information” field refers to the mount point on the owner storage node, so under v8, all you’ve got to do in order to relocate the AFTD is:<\/p>\n This may not seem like a big change, but it’s both useful and more logical. Obviously another benefit of this is that you no longer have to remember device paths when performing manual nsrmm operations against AFTDs \u2013 you just specify the volume name. So your nsrmm commands would go from:<\/p>\n to, in the above example:<\/p>\n The\u00a0real<\/em> benefit of this though is what I’ve been alluding to by talking about the\u00a0first<\/em> mount point specified. You can specify alternate mount points for the device. However, these aren’t additional volumes on the server \u2013 they’re mount points as seen by\u00a0clients<\/em>. This allows a bypass of using nsrmmd to perform a write to a disk backup unit from the client, and instead sees the client write via whatever operating system mount mechanism it’s used (CIFS or NFS).<\/p>\n In this configuration, your disk backup environment can start to look like the following:<\/p>\n\n
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[root@tara usr]# nsrstage -b Default -v -m -S 4244365627<\/strong>\nObtaining media database information on server tara.pmdg.lab\n80470:nsrstage: Following volumes are needed for cloning\n80471:nsrstage: AFTD-B-1 (Regular)\n5874:nsrstage: Automatically copying save sets(s) to other volume(s)\n79633:nsrstage: \nStarting migration operation for Regular save sets...\n6217:nsrstage: ...from storage node: tara.pmdg.lab\n81542:nsrstage: Successfully cloned all requested Regular save sets (with new cloneid)\n 4244365627\/1341909730\n79629:nsrstage: Clones were written to the following volume(s) for Regular save sets:\n 800941L4\n6359:nsrstage: Deleting the successfully cloned save set 4244365627\nRecovering space from volume 15867081 failed with the error 'volume \nmounted on ADV_FILE disk AFTD1 is reading'.\nRefer to the NetWorker log for details.\n89216:nsrd: volume mounted on ADV_FILE disk AFTD1 is reading<\/pre>\n
nsrd NSR info Index Notice: nsrim has finished crosschecking the media db \nnsrd NSR info Media Info: No space was recovered from device AFTD2 since there was no saveset eligible for deletion. \nnsrd NSR info Media Info: No space was recovered from device AFTD4 since there was no saveset eligible for deletion. \nnsrd NSR info Media Info: Deleted 87 MB from save set 4244365627 on volume AFTD-B-1 <\/em>\nnsrd NSR info Media Info: Recovered 87 MB by deleting 1 savesets from device AFTD1. <\/em>\nnsrsnmd NSR warning volume (AFTD-B-1) size is now set to 2868 MB<\/em><\/pre>\n
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# nsrmm -u -f \/d\/backup1<\/strong><\/pre>\n
# nsrmm -u -f AFTD1<\/strong><\/pre>\n