Crash consistent data recovery for ZFS volumes

While TrueNAS® CORE and TrueNAS® Enterprise are more well known for its NAS (network attached storage) prowess, many organizations are also confidently placing their enterprise applications such as hypervisors and databases on TrueNAS® via SANs (storage area networks) as well. Both iSCSI and Fibre Channel™ (selected TrueNAS® Enterprise storage models) protocols are supported well.

To reliably protect these block-based applications via the SAN protocols, ZFS snapshot is the key technology that can be dependent upon to restore the enterprise applications quickly. However, there are still some confusions when it comes to the state of recovery from the ZFS snapshots. On that matter, this situations are not unique to the ZFS environments because as with many other storage technologies, the confusion often stem from the (mis)understanding of the consistency state of the data in the backups and in the snapshots.

Crash Consistency vs Application Consistency

To dispel this misunderstanding, we must first begin with the understanding of a generic filesystem agnostic snapshot. It is a point-in-time copy, just like a data copy on the tape or in the disks or in the cloud backup. It is a complete image of the data and the state of the data at the storage layer at the time the storage snapshot was taken. This means that the data and metadata in this snapshot copy/version has a consistent state at that point in time. This state is frozen for this particular snapshot version, and therefore it is often labeled as “crash consistent“.

In the event of a subsystem (application, compute, storage, rack, site, etc) failure or a power loss, data recovery can be initiated using the last known “crash consistent” state, i.e. restoring from the last good backup or snapshot copy. Depending on applications, operating systems, hypervisors, filesystems and the subsystems (journals, transaction logs, protocol resiliency primitives etc) that are aligned with them, some workloads will just continue from where it stopped. It may already have some recovery mechanisms or these workloads can accept data loss without data corruption and inconsistencies.

Some applications, especially databases, are more sensitive to data and state consistencies. That is because of how these applications are designed. Take for instance, the Oracle® database. When an Oracle® database instance is online, there is an SGA (system global area) which handles all the running mechanics of the database. SGA exists in the memory of the compute along with transaction logs, tablespaces, and open files that represent the Oracle® database instance. From time to time, often measured in seconds, the state of the Oracle® instance and the data it is processing have to be synched to non-volatile, persistent storage. This commit is important to ensure the integrity of the data at all times.

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How well do you know your data and the storage platform that processes the data

Last week was consumed by many conversations on this topic. I was quite jaded, really. Unfortunately many still take a very simplistic view of all the storage technology, or should I say over-marketing of the storage technology. So much so that the end users make incredible assumptions of the benefits of a storage array or software defined storage platform or even cloud storage. And too often caveats of turning on a feature and tuning a configuration to the max are discarded or neglected. Regards for good storage and data management best practices? What’s that?

I share some of my thoughts handling conversations like these and try to set the right expectations rather than overhype a feature or a function in the data storage services.

Complex data networks and the storage services that serve it

I/O Characteristics

Applications and workloads (A&W) read and write from the data storage services platforms. These could be local DAS (direct access storage), network storage arrays in SAN and NAS, and now objects, or from cloud storage services. Regardless of structured or unstructured data, different A&Ws have different behavioural I/O patterns in accessing data from storage. Therefore storage has to be configured at best to match these patterns, so that it can perform optimally for these A&Ws. Without going into deep details, here are a few to think about:

  • Random and Sequential patterns
  • Block sizes of these A&Ws ranging from typically 4K to 1024K.
  • Causal effects of synchronous and asynchronous I/Os to and from the storage

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OpenZFS with Object Storage

At AWS re:Invent last week, Amazon Web Services announced Amazon FSx for OpenZFS. This is the 4th managed service under the Amazon FSx umbrella, joining NetApp® ONTAP™, Lustre and Windows File Server. The highly scalable OpenZFS filesystem can provide high throughput and IOPS bandwidth to Amazon EC2, ECS, EKS and VMware® Cloud on AWS.

I am assuming the AWS OpenZFS uses EBS as the block storage backend, given the announcement that it can deliver 4GB/sec of throughput and 160,000 IOPS from the “drives” without caching. How the OpenZFS is provisioned to the AWS clients is well documented in this blog here. It is an absolutely joy (for me) to see the open source OpenZFS filesystem getting the validation and recognization from AWS. This is one hell of a filesystem.

But this blog isn’t about AWS FSx for OpenZFS with block storage. It is about what is coming, and eventually AWS FSx for OpenZFS could expand into AWS’s proficient S3 storage as well.  Can OpenZFS integrate with an S3 object storage backend? This blog looks into the burning question.

In the recently concluded OpenZFS Developer Summit 2021, one of the topics was “ZFS on Object Storage“, and the short answer is a resounding YES!

OpenZFS Developer Summit 2021

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Right time for Andrew. The Filesystem that is.

I couldn’t hold my excitement when I discovered Auristor® early last week. I stumbled upon this Computerweekly article “Want to side step Public Cloud? Auristor® offers global file storage.” Given the many news not exactly praising the public cloud storage vendors nowadays, the article’s title caught my attention. Immediately Andrew File System (AFS) was there. I was perplexed at first because I have never seen or heard a commercial version of AFS before. This news gave me goosebumps.

For the curious, I am sure many will ask who is this Andrew anyway? What is my relationship with this Andrew?

One time with Andrew

A bit of my history. I recalled quite vividly helping Intel in Penang, Malaysia to implement their globally distributed file caching mechanism with the NetApp® filer’s NFS. It was probably 2001 and I believed Intel wanted to share their engineering computing (EC) files between their US facilities and Intel Penang Design Center (PDC). As I worked along with the Intel folks, I found out that this distributed file caching technology was called Andrew File System (AFS).

Although I couldn’t really recalled how the project went, I remembered it being a bed of bugs at that time. But being the storage geek that I am, I obviously took some time to get to know Andrew the File System. 20 years have gone by, and I never really thought of AFS coming out as a commercial solution or even knew of it as one, until Auristor®,

Auristor Logo

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What happened to NDMP?

The acronym NDMP shows up once in a while in NAS (Network Attached Storage) upgrade tenders. And for the less informed, NDMP (Network Data Management Protocol) was one of the early NAS data management (more like data mover specifications) initiatives to backup NAS devices, especially the NAS appliances that run proprietary operating systems code.

NDMP Logo

Backup software vendors often have agents developed specifically for an operating system or an operating environment. But back in the mid-1990s, 2000s, the internal file structures of these proprietary vendors were less exposed, making it harder for backup vendors to develop agents for them. Furthermore, there was a need to simplify the data movements of NAS files between backup servers and the NAS as a client, to the media servers and eventually to the tape or disk targets. The dominant network at the time ran at 100Mbits/sec.

To overcome this, Network Appliance® and PDC Solutions/Legato® developed the NDMP protocol, allowing proprietary NAS devices to run a standardized client-server architecture with the NDMP server daemon in the NAS and the backup service running as an NDMP client. Here is a simplified look at the NDMP architecture.

NDMP Client-Server Architecture

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Open Source Storage Technology Crafters

The conversation often starts with a challenge. “What’s so great about open source storage technology?

For the casual end users of storage systems, regardless of SAN (definitely not Fibre Channel) or NAS on-premises, or getting “files” from the personal cloud storage like Dropbox, OneDrive et al., there is a strong presumption that open source storage technology is cheap and flaky. This is not helped with the diet of consumer brands of NAS in the market, where the price is cheap, but the storage offering with capabilities, reliability and performance are found to be wanting. Thus this notion floats its way to the business and enterprise users, and often ended up with a negative perception of open source storage technology.

Highway Signpost with Open Source wording

Storage Assemblers

Anybody can “build” a storage system with open source storage software. Put the software together with any commodity x86 server, and it can function with the basic storage services. Most open source storage software can do the job pretty well. However, once the completed storage technology is put together, can it do the job well enough to serve a business critical end user? I have plenty of sob stories from end users I have spoken to in these many years in the industry related to so-called “enterprise” storage vendors. I wrote a few blogs in the past that related to these sad situations:

We have such storage offerings rigged with cybersecurity risks and holes too. In a recent Unit 42 report, 250,000 NAS devices are vulnerable and exposed to the public Internet. The brands in question are mentioned in the report.

I would categorize these as storage assemblers.

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Windows SMB synchronous writes with OpenZFS

Sometimes I get really pissed off with myself because I have taken a bigoted view, and ended up with eggs on my face. The past week was like that, and the problem was gnawing me on the inside all week, because I was determined to balance my equilibrium by finding the answer.

Early in the week, I was having a conversation with a potential customer. It evolved around the missing 10 seconds or so of the video footage between the users of a popular video editing software. The company had 70% Windows users, and 30% users on the Mac, both sides accessing the NAS device. The issue was the editors on the Windows side will store the raw and edited files to the NAS, but when the Mac users read them, they will often find 10 seconds or so of the stored video files missing.

The likeliest culprit of this problem is the way the SMB protocol write I/O behaves in Windows and in MacOS. Windows SMB, by default, writes I/O asynchronously while SMB on MacOS writes I/O synchronously.

I had a strong conviction I had the answer to this issue but this was not a TrueNAS®, It was another brand of NAS that I did not have knowledge of, and so, I left the conversation feeling quite embarrassed because I had the answer only on the TrueNAS® server side, not on the Windows client side. Bigotry blinded me. Hmmph! 

SMB (Server Message Block) client-server model

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SSOT of Files

[ This is part two of “Where are your files living now?”. You can read Part One here ]

Data locality, Data mobility“. It was a term I like to use a lot when describing about data consolidation, leading to my mention about files and folders, and where they live in my previous blog. The thinking of where the files and folders are now as in everywhere as they can be in a plethora of premises stretches the premise of SSOT (Single Source of Truth). And this expatriation of files with minimal checks and balances disturbs me.

A year ago, just before I joined iXsystems, I was given Google® embargoed news, probably a week before they announced BigQuery Omni. Then I was interviewed by Enterprise IT News, a local Malaysian technology news portal to provide an opinion quote. This was what I quoted:

“’The data warehouse in the cloud’ managed services of Big Query is underpinned by Google® Anthos, its hybrid cloud infra and service management platform based on GKE (Google® Kubernetes Engine). The containerised applications, both on-prem and in the multi-clouds, would allow Anthos to secure and orchestrate infra, services and policy management under one roof.”

I further quoted ” The data repositories remain in each cloud is good to address data sovereignty, data security concerns but it did not mention how it addresses “single source of truth” across multi-clouds.

Single Source of Truth – regardless of repositories

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Where are your files living now?

[ This is Part One of a longer conversation ]

EMC2 (before the Dell® acquisition) in the 2000s had a tagline called “Where Information Lives™**. This was before the time of cloud storage. The tagline was an adage of enterprise data storage, proper and contemporaneous to the persistent narrative at the time – Data Consolidation. Within the data consolidation stories, thousands of files and folders moved about the networks of the organizations, from servers to clients, clients to servers. NAS (Network Attached Storage) was, and still is the work horse of many, many organizations.

[ **Side story ] There was an internal anti-EMC joke within NetApp® called “Information has a new address”.

EMC tagline “Where Information Lives”

This was a time where there were almost no concerns about Shadow IT; ransomware were less known; and most importantly, almost everyone knew where their files and folders were, more or less (except in Oil & Gas upstream – to be told in later in this blog). That was because there were concerted attempts to consolidate data, and inadvertently files and folders, in the organization.

Even when these organizations were spread across the world, there were distributed file technologies at the time that could deliver files and folders in an acceptable manner. Definitely not as good as what we have today in a cloudy world, but acceptable. I personally worked a project setting up Andrew File Systems for Intel® in Penang in the mid-90s, almost joined Tacit Networks in the mid-2000s, dabbled on Microsoft® Distributed File System with NetApp® and Windows File Servers while fixing the mountains of issues in deploying the worldwide GUSto (Global Unified Storage) Project in Shell 2006. Somewhere in my chronological listings, Acopia Networks (acquired by F5) and of course, EMC2 Rainfinity and NetApp® NuView OEM, Virtual File Manager.

The point I am trying to make here is most IT organizations had a good grip of where the files and folders were. I do not think this is very true anymore. Do you know where your files and folders are living today? 

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RAIDZ expansion and dRAID excellent OpenZFS adventure

RAID (Redundant Array of Independent Disks) is the foundation of almost every enterprise storage array in existence. Thus a technology change to a RAID implementation is a big deal. In recent weeks, we have witnessed not one, but two seismic development updates to the volume management RAID subsystem of the OpenZFS open source storage platform.

OpenZFS logo

For the uninformed, ZFS is one of the rarities in the storage industry which combines the volume manager and the file system as one. Unlike traditional volume management, ZFS merges both the physical data storage representations (eg. Hard Disk Drives, Solid State Drives) and the logical data structures (eg. RAID stripe, mirror, Z1, Z2, Z3) together with a highly reliable file system that scales. For a storage practitioner like me, working with ZFS is that there is always a “I get it!” moment every time, because the beauty is there are both elegances of power and simplicity rolled into one.

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