If no end time is set then they will be active until they are manually
stopped (or filled 100% then re-written to beginning). We use a copy-on-write technology
below is a description.
Changes are made throughout your schedule to the main volume. If setting up multiple Snapshots try not overlapping them to the same volume. The backup will capture all data that is scheduled in Snapshot so this would be continuous. Try setting end times.
snapshot002 at 8:00 - 12:00
snapshot003 at 12:00 - 18:00
snapshot004 at 18:00 - 23:59
Snapshot technology
Copy-on-write (sometimes referred to as "COW") is an optimization strategy used in computer programming. The fundamental idea is that if multiple callers ask for resources which are initially indistinguishable, you can give them pointers to the same resource. This fiction can be maintained until a caller tries to modify its "copy" of the resource, at which point a true private copy is created to prevent the changes becoming visible to everyone else. All of this happens transparently to the callers. The primary advantage is that if a caller never makes any modifications, no private copy need ever be created.
Copy-on-write finds its main use in virtual memory operating systems; when a process creates a copy of itself, the pages in memory that might be modified by either the process or its copy are marked copy-on-write. When one process modifies the memory, the operating system's kernel intercepts the operation and copies the memory so that changes in one process's memory are not visible to the other.
Another use is in the calloc function. This can be implemented by having a page of physical memory filled with zeroes. When the memory is allocated, the pages returned all refer to the page of zeroes and are all marked as copy-on-write. This way, the amount of physical memory allocated for the process does not increase until data is written. This is typically only done for larger allocations.
Copy-on-write can be implemented by telling the MMU that certain pages in the process's address space are read-only. When data is written to these pages, the MMU raises an exception which is handled by the kernel, which allocates new space in physical memory and makes the page being written to correspond to that new location in physical memory.
One major advantage of COW is the ability to use memory sparsely. Because the usage of physical memory only increases as data is stored in it, very efficient hash tables can be implemented which only use little more physical memory than is necessary to store the objects they contain. However, such programs run the risk of running out of virtual address space -- virtual pages unused by the hash table cannot be used by other parts of the program. The main problem with COW at the kernel level is the complexity it adds, but the concerns are similar to those raised by more basic virtual memory concerns such as swapping pages to disk; when the kernel writes to pages, it must copy them if they are marked copy-on-write. COW is also used outside the kernel, in library, application and system code. The string class provided by C++'s Standard Template Library, for example, was specifically designed to allow copy-on-write implementations. One hazard of COW in these contexts arises in multithreaded code, where the additional locking required for objects in different threads to safely share the same representation can easily outweigh the benefits of the approach. The COW concept is also used in virtualization/emulation software such as Bochs, QEMU, and UML for virtual disk storage. This allows a great reduction in required disk space when multiple VMs can be based on the same hard disk image, as well as increased performance as disk reads can be cached in RAM and subsequent reads served to other VMs out of the cache
Yes you will be able to do a file restore from any snapshot with admin rights that you have assigned. To grant access to the snapshot images you select a user in the SMB Snapshot Access fields. Backing up the snapshots from the will capture all changes made after completion of end time of schedule.
I set up 4 snapshots so that 002 - 004 do not overlap, and each cover a 3 hour 59 minute window.
I have two issues:
1) The drop-list to select the snapshot for local backup shows no entries (Maintenance/Backup/Local Backup/Snapshot). Why?
Also, if I try to backup without any snapshot selected why does a message pop up saying:
"No snapshot choosed.
Backup can be made only from snapshots with no create- and remove-time assigned."
2) Only the active snapshot actually contains files, the other 3 are empty and designated as "unused"
My goal is to have multiple restore points available concurrently. Is this possible?
It would appear that placing an end time on a snapshot causes it to write to the mail volume and "empty" itself. While this is fine, it is not what I need for my implementation.
The obvious solution is to not put end-times on snapshots, which would cause them to persist for 24 hours until refreshed at the next start time. Sounds great, but when you have more than one snapshot in this mode, I need to know how they interact with each other with respect to writes to the main volume. All the questions I asked previously about interaction still apply.
1)
You must set a Snapshot with no begin and no end time. Then create the snapshot in Maintenance / Snapshot this will set it in manual mode to allow you to select from the Maintenance / Backup.
Please read the instructions on how this is done or read the cut that I have provided.
Function “Local backup”
This function allows you to backup shares into tar-gziped files. Available choices:
Source lv:
Please choose logical volume from which shares will be backed up. It is possible
to backup shares from one logical volumes at once.
When you change source lv, avaliable shares and snapshot will also
change.
Snapshot:
Backup is performed from snapshot to provide data integrity.
You can choose only from snapshots with no create- and remove-time
assigned.
2)
You can have multiple snapshots to provide multiple restore points. Please set your Snapshots appropriate to the scheduled or with no end time for file recovery purposes. It would be best if you can test which Snapshot functions would best fit your needs for this, as every environment is different.
I think I understand snapshots well enough now to know that I want to have no end times in order to preserve restorable data. This gives me snapshots that are refreshed at create time every day. Cool.
The only issue I have now is with backups. You've confirmed that backups can only function on snapshots that have no start or end time. That means no automatically scheduled snapshot can be backed up at all, -only manually created ones.
Reply With Quote