Umem™ cards are battery-backed RAM cards that replace disk accesses with non-volatile memory accesses to improve response time and maintain reliability in server and storage appliances.

Teamed with the founders of Legato™, Micro Memory designed the original Umem cards for Prestoserve™, the ubiquitous host write-caching software module OEM’d by companies such as Compaq, DEC, IBM, and Sun Microsystems.

Since its inception in 1976, Micro Memory has specialized in designing and manufacturing battery backed RAM cards for open industry standard bus architectures.  This has involved pioneering a myriad of data retention features and over twenty-five years of refining the battery failover circuitry for use in enterprise products and high availability solutions.

Especially applicable to file servers and storage appliances that adhere to the NFS protocol or utilize journaling filesystems, Umem cards enable these products to improve performance for I/O intensive applications and still comply with the industry standard benchmark, SPEC SFS.

SPEC SFS requires following the NFS protocol, which ensures reliability by making many operations synchronous.  These operations typically involve directory and inode updates, journal logs and metadata, data base snapshots, cluster check points, time stamps and changes to actual file data.

Specifically, this means that when a client issues a synchronous write or commit request to the server/storage appliance, the server cannot reply back to the client that the request has been received until the write has been committed to stable storage.  This can also prevent the client from initiating new requests until it receives the required acknowledgment.  As most networks have several clients, this can easily create a bottleneck in terms of response time.

While making operations synchronous and requiring they be committed to stable storage is an excellent method towards guaranteeing reliability, there is an associated performance penalty.  This penalty is greatest when hard disk drive(s) are selected as the stable storage device.

Umem PCI NVRAM cards minimize this penalty and response time by replacing disk accesses with memory accesses; SDRAM memory accesses are generally several million times faster than any hard disk drive.  But unlike system memory, the Umem cards uniquely provide on-board battery back-up that enables data retention and prevents re-initialization of memory upon power up or system reset, complying with the NFS protocol and SpecSFS requirements for stable storage.

PCI NVRAM vs. Storage Controller NVRAM
Unlike NVRAM that resides on a storage controller, PCI NVRAM can be completely controlled by the host that is also controlling the filesystem, volume manager, or clustering services.  As such, host NVRAM can be used more intelligently and efficiently than NVRAM on a storage controller because it can be accessed at either the file level or the block level.

PCI NVRAM also provides superior performance to NVRAM on external storage controllers for synchronous writes because it is only limited by bus speeds.  NVRAM on external storage devices is accessed indirectly with SCSI commands and limited by the significant overhead of a cable interconnect. (for a detailed white paper on this topic contact sales@micromemory.com and include “PCI NVRAM vs. Storage Controller NVRAM” in the subject header)

PCI NVRAM vs. System Memory with UPS
Because software errors are more likely to be the cause of system failures than hardware errors, relying on a UPS is generally not considered an optimal alternative for ensuring data reliability in mid-range and enterprise products.  UPS implementations require complicated modifications to the host operating system, can require boot PROM bios changes, and difficult kernel mapping issues.  As UPS’s do not scale linearly, they inherently conflict with many of the guiding principles behind utility storage and modular appliances. (for a detailed white paper on this topic contact sales@micromemory.com and include “PCI NVRAM vs. System Memory with UPS” in the subject header)

Journaling Filesystems
Several journaling filesystems now provide external journal mounts, so the journal log (metadata) can easily be placed on a separate device.  Due to the nature of journal updates which often involve small, frequent writes where disk performance is at its lowest, a high speed PCI NVRAM card can be used as the device for the journal log.

Some journaling filesystems also have a mode in which all data is journaled, including metadata and actual file data.  These systems provide an additional level of data protection, but this usually comes at the expense of increased disk operations.  Using a PCI NVRAM device in this mode increases system performance and maintains or improves data reliability while providing protection of data as well as consistency of the filesystem. (for a detailed white paper on this topic contact sales@micromemory.com and include “Journaling Filesystems” in the subject header)

Clustered Umem NVRAM Cards
Micro Memory has pioneered an innovative implementation of host based NVRAM cards for Clustered Failover in scalable, highly available systems.  Cards can communicate, mirror or failover data in clustered configurations after or during a primary system failure, regardless of power loss.  Combined with the CacheOver™ system, a thin layer service can be incorporated below generally available, comprehensive clustering software to provide the ultimate in performance and availability. (for more information on this product line contact sales@micromemory.com and include “CacheOver” in the subject header)