Part II: IBM Server Side Storage I/O SSD Flash Cache Software

Part II IBM Server Flash Cache Storage I/O accelerator for SSD

This is the second in a two-part post series on IBM’s Flash Cache Storage Accelerator (FCSA) for Solid State Device (SSD) storage announced today. You can view part I of the IBM FCSA announcement synopsis here.

Some FCSA ssd cache questions and perspectives

What is FCSA?
FCSA is a server-side storage I/O or IOP caching software tool that makes use of local (server-side) nand flash SSD (PCIe cards or drives). As a cache tool (view IBM flash site here) FCSA provides persistent read caching on IBM servers (xSeries, Flex and Blade x86 based systems) with write through cache (e.g. data cached for later reads) while write data is written directly to block attached storage including SANs. back-end storage can be iSCSI, SAS, FC or FCoE based block systems from IBM or others including all SSD, hybrid SSD or traditional HDD based solutions from IBM and others.

How is this different from just using a dedicated PCIe nand flash SSD card?
FCSA complements those by using them as a persistent storage to cache storage I/O reads to boost performance. By using the PCIe nand flash card or SSD drives, FCSA and other storage I/O cache optimization tools free up valuable server-side DRAM from having to be used as a read cache on the servers. On the other hand, caching tools such as FCSA also keep local cached reads closer to the applications on the servers (e.g. locality of reference) reducing the impact on backed shared block storage systems.

What is FCSA for?
With storage I/O or IOPS and application performance in general, location matters due to locality of reference hence the need for using different approaches for various environments. IBM FCSA is a storage I/O caching software technology that reduces the impact of applications having to do random read operations. In addition to caching reads, FCSA also has a write-through cache, which means that while data written to back-end block storage including on iSCSI, SAS, FC or FCoE based storage (IBM or other vendors), a copy of the data is cached for later reads. Thus while the best storage I/O is the one that does not have to be done (e.g. can be resolved from cache), the second best would be writes that go to a storage system that are not competing with read requests (handled via cache).

Who else is doing this?
This is similar to what EMC initially announced and released in February 2012 with VFcache now renamed to be XtremSW along with other caching and IO optimization software from others (e.g. SANdisk, Proximal and Pernix among others.

Does this replace IBM EasyTier?
Simple answer is no, one is for tiering (e.g. EasyTier), the other is for IO caching and optimization (e.g. FCSA).

Does this replace or compete with other IBM SSD technologies?
With anything, it is possible to find a way to make or view it as competitive. However in general FCSA complements other IBM storage I/O optimization and management software tools such as EasyTier as well as leverage and coexist with their various SSD products (from PCIe cards to drives to drive shelves to all SSD and hybrid SSD solutions).

How does FCSA work?
The FCSA software works in either a physical machine (PM) bare metal mode with Microsoft Windows operating systems (OS) such as Server 2008, 2012 among others. There is also *nix support for RedHat Linux, along with in a VMware virtual machine (VM) environment. In a VMware environment High Availability (HA), DRS and VMotion services and capabilities are supported. Hopefully it will be sooner vs. later that we hear IBM do a follow-up announcement (pure speculation and wishful thinking) on more hypervisors (e.g. Hyper-V, Xen, KVM) support along with Centos, Ubuntu or Power based systems including IBM pSeries. Read more about IBM Pure and Flex systems here.

What about server CPU and DRAM overhead?
As should be expected, a minimal amount of server DRAM (e.g. main memory) and CPU processing cycles are used to support the FCSA software and its drivers. Note the reason I say as should be expected is how you can have software running on a server doing any type of work that does not need some amount of DRAM and processing cycles. Granted some vendors will try to spin and say that there is no server-side DRAM or CPU consumed which would be true if they are completely external to the server (VM or PM). The important thing is to understand how much of an impact in terms of CPU along with DRAM consumed along with their corresponding effectiveness benefit that are derived.

Does FCSA work with NAS (NFS or CIFS) back-end storage?
No this is a server-side block only cache solution. However having said that, if your applications or server are presenting shared storage to others (e.g. out the front-end) as NAS (NFS, CIFS, HDFS) using block storage (back-end), then FCSA can cache the storage I/O going to those back-end block devices.

Is this an appliance?
Short and simple answer is no, however I would not be surprised to hear some creative software defined marketer try to spin it as a flash cache software appliance. What this means is that FCSA is simply IO and storage optimization software for caching to boost read performance for VM and PM servers.

What is this hardware or storage agnostic stuff mean?
Simple, it means that FCSA can work with various nand flash PCIe cards or flash SSD drives installed in servers, as well as with various back-end block storage including SAN from IBM or others. This includes being able to use block storage using iSCSI, SAS, FC or FCoE attached storage.

What is the difference between Easytier and FCSA?
Simple, FCSA is providing read acceleration via caching which in turn should offload some reads from affecting storage systems so that they can focus on handling writes or read ahead operations. Easytier on the other hand is for as its name implies tiering or movement of data in a more deterministic fashion.

How do you get FCSA?
It is software that you buy from IBM that runs on an IBM x86 based server. It is licensed on a per server basis including one-year service and support. IBM has also indicated that they have volume or multiple servers based licensing options.

Does this mean IBM is competing with other software based IO optimization and cache tool vendors?
IBM is focusing on selling and adding value to their server solutions. Thus while you can buy the software from IBM for their servers (e.g. no bundling required), you cannot buy the software to run on your AMD/Seamicro, Cisco (including EMC/VCE and NetApp) , Dell, Fujitsu, HDS, HP, Lenovo, Oracle, SuperMicro among other vendors servers.

Will this work on non-IBM servers?
IBM is only supporting FCSA on IBM x86 based servers; however, you can buy the software without having to buy a solution bundle (e.g. servers or storage).

What is this Cooperative Caching stuff?
Cooperative caching takes the next step from simple read cache with write-through to also support chance coherency in a shared environment, as well as leverage tighter application or guest operating system and storage system integration. For example, applications can work with storage systems to make intelligent predictive informed decisions on what to pre-fetch or read ahead and cached, as well as enable cache warming on restart. Another example is where in a shared storage environment if one server makes a change to a shared LUN or volume that the local server-side caches are also updated to prevent stale or inconsistent reads from occurring.

Can FCSA use multiple nand flash SSD devices on the same server?
Yes, IBM FCSA supports use of multiple server-side PCIe and or drive based SSD devices.

How is cache coherency maintained including during a reboot?
While data stored in the nand flash SSD device is persistent, it’s up to the server and applications working with the storage systems to decide if there is coherent or stale data that needs to be refreshed. Likewise, since FCSA is server-side and back-end storage system or SAN agnostic, without cooperative caching it will not know if the underlying data for a storage volume changed without being notified from another server that modified it. Thus if using shared back-end including SAN storage, do your due diligence to make sure multi-host access to the same LUN’s or volumes is being coordinated with some server-side software to support cache coherency, something that would apply to all vendors.

What about cache warming or reloading of the read cache?
Some vendors who have tightly interested caching software and storage systems, something IBM refers to as cooperative caching that can have the ability to re-warm the cache. With solutions that support cache re-warming, the cache software and storage systems work together to main cache coherency while pre-loading data from the underlying storage system based on hot bands or other profiles and experience. As of this announcement, FCSA does not support cache warming on its own.

Does IBM have service or tools to complement FCSA?
Yes, IBM has an assessment, profile and planning tool that are available on a free consultation services basis with a technician to check your environment. Of course, the next logical step would be for IBM to make the tool available via free download or on some other basis as well.

Do I recommend and have I tried FCSA?
On paper, or WebEx, YouTube or other venue FCSA looks interesting and capable, a good fit for some environments particular if IBM server-based. However since my PM and VMware VM based servers are from other vendors, along with the fact that FCSA only runs on IBM servers, have not actually given it a hands on test drive yet. Thus if you are looking at storage I/O optimization and caching software tools for your VM or PM environment, checkout IBM FCSA to see if it meets your needs.

General comments

It is great to see server and storage systems vendors add value to their solutions with I/O and performance optimization as well as caching software tools. However, I am also concerned with the growing numbers of different software tools that only work with one vendor’s servers or storage systems, or at least are supported as such.

This reminds me of a time not all that long ago (ok, for some longer than others) when we had a proliferation of different host bus adapter (HBA) driver and pathing drivers from various vendors. The result is a hodge podge (a technical term) of software running on different operating systems, hypervisors, PM’s, VMs, and storage systems, all of which need to be managed. On the other hand, for the time being perhaps the benefit will outweigh the pain of having different tools. That is where there are options from server-side vendor centric, storage system focused, or third-party software tool providers.

Another consideration is that some tools work in VMware environments; others support multiple hypervisors while others also support bare metal servers or PMs. Which applies to your environment will of course depend. After all, if you are an all VMware environment given that many of the caching tools tend to be VMware focused, that gives more options vs. for those who are still predominately PM environments.

Ok, nuff said (for now)

Cheers
Gs

Greg Schulz – Author Cloud and Virtual Data Storage Networking (CRC Press), The Green and Virtual Data Center (CRC Press) and Resilient Storage Networks (Elsevier)

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