The Azure Service Fabric appears to be focused on scenarios in which all data can fit within RAM and persistence is used as a backing store. Reliable Services are designed to store information in Reliable Collections, which use a log-checkpoint system where logged information is written into RAM. Meanwhile, for Reliable Actors, the default actor state provider is "the distributed Key-Value store provided by Service Fabric platform." This seems to indicate that the same limitations would apply.
There may, however, be situations in which one would like to use the Service Fabric for "hot data" but write "cold data" to some form of permanent storage. What are best practices for handling this transition?
In Orleans, this seems to be handled automatically, using a persistence store such as Azure tables. But it seems that a principal design purpose of the Service Fabric and the Reliable Collections are to avoid needing external services, thus enhancing data locality. The current documentation anticipates the possibility that one would want to move data into some permanent store for disaster recovery and analytics, but it does not discuss the possibility of moving data back and forth between persistence-backed in-memory actors and more permanent forms of storage.
A possible answer is that the Service Fabric already does this. Maybe a Reliable Dictionary has some built-in mechanism for switching between persistence-backed in-memory storage and permanent storage.
Or, maybe the answer is that one must manage this oneself. One approach might be for an Actor to keep track of how "hot" it is and switch its persistence store as necessary. But this sacrifices one of the benefits of the Actor model, the automatic allocation and deallocation of actors. Similarly, we might periodically remove items from the Reliable Dictionary and add it to some other persistence store, and then add them back. Again, though, this requires knowledge of when it makes sense to make the transition.
A couple of examples may help crystallize this:
(1) Suppose that we are implementing a multiplayer game with many different "rooms." We don't need all the rooms in memory at once, but we need to move them into memory and use local persistence as a backup once players join them.
(2) Suppose that we are implementing an append-only B-Tree as part of a database. The temptation would be to have each B-Tree node be a stateful actor. We would like hot b-trees to remain in memory but of course the entire index can't be in memory. It seems that this is a core scenario that is already implemented for things like DocumentDB, but it's not clear to me from the documentation how one would do this.
A related question that I found is here. But that question focuses on when to use Azure Service Fabric vs. external services. My question is on whether there is a need to transition between them, or whether Azure Service Fabric already has all the capability needed here.
The Key-Value store state provider does not require everything to be kept in memory. This provider actually stores the state of all actors on the local disk and the state is also replicated to the local disk on other nodes. So the KVS store is considered a persistent and reliable store.
In addition to that, the state of active actors is also stored in memory. When an actor hasn't been used in a while, it gets deactivated and garbage collected. When this happens, the in-memory copy is freed and only the copy on disk remains. When the actor is activated again, the state is fetched from disk and remains in memory as long as the actor is active.
Also, KVS is not the only built-in state provider. We also have the VolatileActorStateProvider (http://azure.microsoft.com/en-gb/documentation/articles/service-fabric-reliable-actors-platform/#actor-state-provider-choices). This is the state provider that keeps everything in memory.
The KvsActorStateProvider does indeed store actor state in a KeyValueStore which is a similar structure to the ReliableDictionary.
The first question I'd ask is whether you need to relegate old actors state to cold storage? The limitation of keeping everything in memory doesn't limit you to a total number of actors, but a total number per replica. So you must first consider the partitioning strategy so that your actors are distributed across a number of different replicas. As your demands grow you can then add more machines to the cluster and the ServiceFabric will orchestrate movements of the replicas to the new machines. For more information on partitioning of the Actor service, see http://azure.microsoft.com/en-gb/documentation/articles/service-fabric-reliable-actors-platform/
If you do want to use cold storage after some time, then you have a couple of options. Firstly, you could decorate your actors with a custom ActorStateProviderAttribute that returns your own implementation of an IActorStateProvider that can handle persistence as you decide.
Alternatively, you could handle it entirely within your Actor implementation. Hook into the Actor Lifecycle and in OnDeactivateAsync such that when the instance is garbage collected, or use an Actor Reminder for some specified time in the future, to serialise the state and store in cold storage such as blob or table storage and null out the State property. The ActivateAsync override can then be used to retrieve this state from offline storage and deserialise.
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Could someone explain what difference between Object Storage and File Storage is please?
I read about Object Storage on wiki, also I read http://www.dell.com/downloads/global/products/pvaul/en/object-storage-overview.pdf, also I read amazons docs(S3), openstack swift and etc. But could someone give me an example to understand better?
All the difference is only that for 'object storage' objects we add more metadata?
For example how to store image like object using some programming language (for example python)?
Thanks.
IMO, Object storage has nothing to do with scale because someone could build a FS which is capable of storing a huge number of files, even in a single directory.
It is also not about the access methods. HTTP access to data in filesystems has been available in many well known NAS systems.
Storage/Access by OID is a way to handle data without bothering about naming it. It could be done on files too. I believe there is an NFS protocol extension that allows this.
I would muster this: Object storage is a (new/different) ''object centric'' way of thinking of data, its access and management.
Think about these points:
What are snapshots today? They are point in time copies of a volume. When a snapshot is taken, all files in the volume are snapped too. Whether all of them like it or not, whether all of them need it or not. A lot of space can get used(wasted?) for a complete volume snapshot while only a few files needed to be snapped.
In an object storage system, you will rarely see snapshots of volumes, objects will be snapshot-ed, perhaps automatically. This is object versioning. All objects need not be versioned, each individual object can tell if it is versioned.
How are files/volumes protected from a disaster? Typically, in a Disaster Recovery(DR) setup, entire volumes/volume-sets are setup for replication to a DR site. Again, this does not bother whether individual files want to be replicated or not. The unit of disaster protection is the volume. Files are small fry.
In an object storage system, DR is not volume centric. Object metadata can decide how many copies should exist and where(geo locations/fault domains).
Similarly for other features:
Tiering - Objects placed in storage tiers/classes based on its metadata independent of other unrelated objects.
Life - Objects move between tiers, change the number of copies, etc, individually, instead of as a group.
Authentication - Individual objects can get authenticated from different authentication domains if required.
As you can see, the change in thinking is that in an object store, everything is about an object.
Contrast this with the traditional way of thinking about and management and access larger containers like volumes(containing files) is not object storage.
The features above and their object-centric-ness fits well with the requirements of unstructured data and hence the interest.
If a storage system is object(or file) centric instead of volume centric in its thinking, (irrespective of the access protocol or the scale,) it is an object storage system.
Disclosure - I work for a vendor (NetApp) that develops and sells both large filesystem and object storage platforms, I'll try to keep this as implementation neutral as I can, but my cognitive biases may unconciously influence my answer.
There are many differences from both an access, programmability and implementation point of view, however given this is likely to be read primarily by programmers rather than infrastructure or storage people, I’ll focus on that aspect here.
The main difference from an external / programming point of view, is that an object in an object store is created or deleted or updated as a complete unit, you can't append data to an object and you can't update a portion of an object "in place", you can however replace it while still keeping the same object ID. Creating, Reading, Updating and Deleting objects is typically done via relatively straightforward APIs, which are almost always REST-ful or REST based and encourages a mindset that the store is a programmable resource or perhaps as multi-tenant remote service. While most of the object stores I'm aware of support byte-range reads within an object, in general objects stores were initially designed to work with whole objects . Good examples of object storage API’s are those used by Amazon S3 (the default standard for object storage access), OpenStack Swift, and Azure Blob Service REST API. Describing the back end implementations behind these APIs would be a book all by itself.
On the other hand files in a filesystem have a broader set of functions that can be applied to them, including appending data, and updating data in place. The programming model is more complex than an object store and is now almost always accessed programatically via a "POSIX" style of interface and generally tries to make the most efficient use of CPU and memory and encourages a mindset that the filesystem is a private local resource. NFS and SMB does allow for a filesystem to be made available as a multi-tenanted resource, however these are often treated with suspicion by programmers as they sometimes have subtle differences in how they react compared to "local" filesystems despite their full support for POSIX semantics. To update files in a local filesystem, you will probably use API’s such as https://www.classes.cs.uchicago.edu/archive/2017/winter/51081-1/LabFAQ/lab2/fileio.html or https://msdn.microsoft.com/en-us/library/mt794711(v=vs.85).aspx. Talking about the relative merits of filesystem implementations e.g. NTFS vs BTRFS vs XFS vs WAFL vs ZFS has a tendency to result in a religious war that is rarely worth anyones time, though if you buy me a beer I’ll happily share my opinions with you.
From a use-case point of view, if you wanted to keep a large number of photo’s, or videos, or binary build artefacts, then an object store is often a good choice. If on the other hand you wanted to persistently store data in a binary tree and update that data in place on the storage media then an object store simply wouldn’t work, and you’d be much better off with a filesystem (you could also use raw block devices for that, but I haven’t seen anybody do that since the early 90s)
The other big differences are that filesystems a designed to be strongly consistent, and are usually accessed over low to moderate latency (50 microseconds - 50 milliseconds) networks whereas object stores are often eventually consistent, and distributed over a shared nothing infrastructure connected together over low bandwidth high latency wide area networks and their time to first byte can sometimes be measured in multiples of whole seconds. Performing lots of small (4K - 16K) random reads from an object store is likely to cause frustration and performance problems.
The other main benefit of an object store vs a filesystem is that you can be reasonably sure that anything you put in an object store will remain there until you ask for it again and that it will never run out of space so long as you keep paying for the monthly charges. These resources are generally run at large scale with built in replication, version control, automated recovery etc etc and nothing short of Hurricane Harvey style disaster will make the data disappear (even then, you have easy options to make another copy in another location). With a filesystem, especially one that you are expecting you or your local operations people to manage, you have to hope that everything is getting backed up and that it doesnt fill up accidentally and cause everything to melt down when you cant update your data anymore.
I've tried to be conscise, but to add to the confusion the words "filesystem" and "object store” get applied to things which are nothing like the descriptions I’ve used above, e.g. NFS the Network file system isn’t actually a filesystem, its a way of implementing the posix storage API’s via remote procedure calls, and VMware’s VSAN stores its data in something they refer to as an "object store" which allows high speed in place updates of the virtual machine images.
There are some very fundamental differences between File Storage and Object Storage.
File storage presents itself as a file system hierarchy with directories, sub-directories and files. It is great and works beautifully when the number of files is not very large. It also works well when you know exactly where your files are stored.
Object storage, on the other hand, typically presents itself via. a RESTful API. There is no concept of a file system. Instead, an application would save a object (files + additional metadata) to the object store via. the PUT API and the object storage would save the object somewhere in the system. The object storage platform would give the application a unique key (analogous to a valet ticket) for that object which the application would store in the application database. If an application wanted to fetch that object, all they would need to do is give the key as part of the GET API and the object would be fetched by the object storage.
Hope this is now clear.
The simple answer is that object accessed storage systems or services utilize APIs and other object access methods for storing, retrieving and looking up data as opposed to traditional file or NAS. For example with file or NAS, you access storage using NFS (Network File System) or CIFS (e.g. windows file share) aka SMB aka SAMBA where the file has a name/handle with associated meta data determined by the file system.
The meta data includes info about create, access, modified and other dates, permissions, security, application or file type, or other attributes. Files are limited by the file system in terms of their size, as well as the number of files per file system. Likewise, file systems are limited by their total or aggregate size in terms of space capacity and the number of files in the filesystem.
Object access is different in that while file or NAS front-end or gateways or plugins are available for many solutions or services, primary access is via an API where an object can be of arbitrary size (up to the maximum of the object system) along with variable sized meta data (depends on the object system/service implementation). With most object storage systems/services you can specify anywhere from a few Kbytes of user defined meta data or GBytes. What would you use GBytes of meta data for? How about in addition to normal info, adding more data for policies, managements, where other copies are located, thumbnails or small previews of videos, audio, etc.
Some examples of object access APIs or interfaces include Amazon Web Services (AWS) simple storage services (S3) or other HTTP and REST based ones, SNIA CDMI. Different solutions will also support IOS (e.g. iphone/ipad) access, SOAP, Torrent, WebDav, JSON, XAM among others plus NFS/CIFS. In addition many of the object storage systems or services support programmatic bindings for python among others. The APIs allow you to essentially open a stream and then get or put, list and other functions supported by the API/system to determine how you will use it.
For example, I use both Rackspace Cloud files and Amazon S3 (in addition to EBS and Glacier) for backing up, storing, and archiving data. I can access the objects stored via a web browser or tools including Jungle disk (JD) which is what I backup and synchronize files with. JD handles the object management and moves data to both Rackspace as well as Amazon for me. If I were inclined, I could also do some programming using the APIs and then directly access either of those sites supplying my security credentials to do things with my stored objects.
Here is a link to object and cloud storage primer from a session I did in Holland last year that has some simple examples of objects and access.
http://storageio.com/DownloadItems/Nijkerk_Nov2012/SIO_IndustryTrends_CloudObjectStorage.pdf
Using the programmatic binding, you would define your data structures or objects in your program and then use the APIs or calls for storing, retrieving, listing of data, meta data access etc. If there is a particular object storage system, software or service that you are looking to work with or need to know how to program to, go to their site and you should find their SDK or API info with examples. With objects, once you create your initial bucket or container on a service or with a product/system, you then simply create and store additional objects as you go.
Here is a link as an example to AWS S3 API/programming:
http://docs.aws.amazon.com/AmazonS3/latest/API/IntroductionAPI.html
In theory object storage systems are talked about has having unlimited numbers of objects, or object size, in reality, most systems, solutions, software or services are limited by what they have either tested or currently support, which can be billions of objects, with objects sizes of 5GByte or larger. Pay attention to the limits on specific services or products as to what is actually tested, supported vs. what is architecturally possible or what is implemented on webex or powerpoint.
Again its very service and product/service/software dependent as to the number of objects, size of the objects, size of meta data, and amount of data that can be moved in/out via their APIs. However, it is generally safe to assume that object storage can be much more scalable (depending on implementation) than file systems (without using global name space, federation, file virtualization or other techniques).
Also in my book Cloud and Virtual Data Storage Networking (CRC Press) that is Intel Recommended Reading, you will find more information about cloud and object storage.
I will be adding more related material to www.objectstorage.us soon.
Cheers gs
Object Storage = Block Storage
+ Rich Metadata
- File hierarchy
Block Storage uses a filesystem to point where content is stored.
Object Storage uses a identifyer to point to content and his context.
This is my understanding of reading Content-addressed vs. location-addressed
Block Storage needs a filesystem and structuring so with bigger files sytems comes more overhead.
The Object storage has a lot of context about the file and doesn't need the file hierarchy.
The explanation on page 7 of the Dell paper clearly shows this..What troubled me to, was that on the scale of the hard disk itself it isn't explained.
I found that a Hard Disk itself always uses a Block storage mechanism (though that seems to be changing to)
(though that seems to be changing to)
some other insights can be found here
This answer doesn't even explain anything about the differences.
There are some very fundamental differences between File Storage and Object Storage.
File storage presents itself as a file system hierarchy with directories, sub-directories and files. It is great and works beautifully when the number of files is not very large. It also works well when you know exactly where your files are stored.
Object storage, on the other hand, typically presents itself via. a RESTful API. There is no concept of a file system. Instead, an application would save a object (files + additional metadata) to the object store via. the PUT API and the object storage would save the object somewhere in the system. The object storage platform would give the application a unique key (analogous to a valet ticket) for that object which the application would store in the application database. If an application wanted to fetch that object, all they would need to do is give the key as part of the GET API and the object would be fetched by the object storage.
This explained a large portion of it; but you argued about the meta data.
Object storage has no sense of folders, or any kind of organization structure which makes it easy for a human to organize. File Storage, of course, does have all those folders that make it so easy for a human to organize and shuffle through...In a server environment with the number of files in a scale that is astronomical, folders are just a waste of space and time.
Databases you say? Well they're not talking about the Object storage itself, they are saying your http service (php, webmail, etc) has the unique ID in its database to reference a file that may have a human recognizable name.
Metadata, well where is this file stored you say? That's what the metadata is for. Your single file is split up into a bunch of small pieces and spread out of geographic location, servers, and hard drives. These small pieces also contain more data, they contain parity information for the other pieces of data, or maybe even outright duplication.
The metadata is used to locate every piece of data for that file over different geographic locations, data centres, servers and hard drives as well as being used to restore any destroyed pieces from hardware failure. It does this automatically. It will even fluidly move these pieces around to have a better spread. It will even recreate a piece that is gone and store it on a new good hard drive.
This maybe a simple explanation; but I think it might help you better understand. I believe file storage can do the same thing with the metadata; but file storage is storage that you can organize as a human (folders, hierarchy and such) whereas object storage has no hierarchy, no folders, just a flat storage container.
Actually you can mount an bucket/container and access the objects or subfolders (and their objects) from Linux. For example, I have s3fs installed on Ubuntu that I have setup a mount point to one of my S3 buckets and able to do regular cp, ls and other functions just as though it were another filesystem. The key is getting the software tool of which there are plenty that allows you to map a bucket/container and present it as mount point. There are also software tools that allow you to access S3 and other buckets/containers via iSCSI in addition to as NAS.
Most companies with object based solutions have a mix of block/file/object storage chosen based on performance/cost reqs.
From a use case perspective:
Ultimately object storage was created to address unstructured data which is growing explosively, far quicker than structured data.
For example, if a database is structured data, unstructured would be a word doc or PDF.
How do you search 1 billion PDFs in a file system? (if it could even store that many in the first place).
How quickly could you search just the metadata of 1 billion files?
Object storage is currently used more for long term or archival, cheap and deep storage, that keeps track of more detail of what that data is. This metadata becomes very powerful when searching or mining very large data sets. Sometimes you can get what you need from the metadata without even accessing the data itself. Object storage solutions can typically replicate automatically with geographic failover built-in.
The problem is that application would have to be re-written to use object access methods rather than file hierarchy (which is simpler from a app dev perspective). It's really a change in the philosophy of data storage, and storing more actionable information about that data from a management standpoint as well as usage.
Quick example might be an MRI scan image. On Filesystem you have owner/creation date, but not much else. If it were an object, all of the information surrounding the MRI could be stored along with it in metadata, like patient name, MRI center location, the requesting Dr., insurance carrier, etc.
Block/file are more well suited for local access or OTLP where performance is more important than retention and cost.
For example, you would not want to wait minutes for a Word doc to open, but you could wait a few minutes for a data mining/business intelligence process to complete.
Another example would be a legal search where you have to search everything from 5 years ago to present. With retention policies in place to decrease the active data set and cost, how would you even do that without restoring from tape?
Object storage is a great solution for replacing long term archival methods like tape.
Setting up replication and failover for block and file can get very expensive in the enterprise and usually requires very expensive software and services.
Note: At the lower level, object storage access happens via the RESTful API which is more like a web request than accessing a file at the end of a path.
Here is a good article worth to read:
https://cloudian.com/blog/object-storage-vs-file-storage/
cited from the ariticle:
To start, object storage overcomes many of the limitations that file storage faces. Think of file storage as a warehouse. When you first put a box of files in there, it seems like you have plenty of space. But as your data needs grow, you’ll fill up the warehouse to capacity before you know it. Object storage, on the other hand, is like the warehouse, except with no roof. You can keep adding data infinitely – the sky’s the limit.
If you’re primarily retrieving smaller or individual files, then file storage shines with performance, especially with relatively low amounts of data. Once you start scaling, though, you may start wondering, “How am I going to find the file I need?”
In this case, you can think of object storage as valet parking while file storage is more like self-parking (yes, another analogy, but bear with me!). When you pull your car into a small lot, you know exactly where your car is. However, imagine that lot was a thousand times larger – it’d be harder to find your car, right?
Because object storage has customizable metadata and all the objects live on a flat address space, it’s similar to handing your keys over to a valet. Your car will be stored somewhere, and when you need it, the valet will get the car for you. It might take a little longer to retrieve your car, but you don’t have to worry about wandering around looking for it.
I think the white paper explains the idea of object storage quite well. I am not aware of any standard way to use object storage devices (in the sense of a SCSI OSD) from a user application.
Object storage is in use in some large scale storage products like the storage appliances of Panasas. However, these appliances then export a file system to the end user. It is IMHO fair to say that the T10 OSD idea never really caught momentum.
Related ideas to the OSD standard can be found in cloud storage systems like S3 and RADOS.