|
|
|
|
Tom Hotle
Disk products that are currently supported on Silicon Graphics' Cray GigaRing I/O systems include several interfaces, disk sizes, and rotation speeds. This variety has evolved from the need to provide cost effective and high performance solutions, and from the evolution of disk technology over the time frame supported by GigaRing I/O systems. Table 1 lists the disk drives that are supported on GigaRing I/O systems, including new products and products that are supported in migration from previous generation Model E IOS systems.
| RPM | Disk Size | Capacity | Disk BW | FCS | ||
|---|---|---|---|---|---|---|
| IPI | DD-60 | 3600 | 8" | 1.9 GB | 20 MB/s | 1991 |
| DD-62 | 4365 | 8" | 2.7 GB | 8 MB/s | 1992 | |
| DD-301 | 5400 | 3.5" | 1.4 GB | 8 MB/s | 1994 | |
| DD-302 | 5400 | 3.5" | 1.8 GB | 9 MB/s | 1995 | |
| SCSI | DD-6s | 5400 | 5.25 | 9 GB | 4.5 - 7 MB/s | 1995 |
| DD-314 | 7200 | 3.5" | 4.5 GB | 5 - 7.5 MB/s | 1996 | |
| DD-318 | 7200 | 3.5" | 9.5 GB | 7 - 12 MB/s | 1997 | |
| Fibre Channel | DD-308 | 7200 | 3.5" | 9.5 GB | 7 - 12 MB/s | 1997 |
Three interface types are supported. SCSI interface devices are provided to allow the attachment of cost effective devices. The Fibre Channel interface was chosen to provide high performance connections. The IPI interface is included to allow migration of disks from previous generation Model E IOS systems.
Disk sizes in Table 1 vary from 8-inch DD-60 and DD-62 devices to 3.5-inch disks on DD-314, DD-318, DD-308, and DD-301 and DD-302. The 8-inch disk products are older devices that were introduced on Model E IOS systems as early as 1991, but many are still in service on GigaRing systems. Disk capacities vary from 1.4 GB on DD-301s to 9 GB on DD-318s and DD-308s. Disk transfer rates range from 7 MB/s on the DD-6s drives to 20 MB/s on DD-60s.
The Fibre Channel and IPI interface disk drives in Table 1 can be attached in either JBOD (Just a Bunch of Disks) or arrays. Arrays are chosen to achieve higher bandwidth and data reliability. Table 2 lists the arrays that can be configured on GigaRing systems.
| Interface | Array Capacity | Peak Array Bandwidth (Read) |
Array Configuration |
Peak Node Bandwidth (Read) |
|
|---|---|---|---|---|---|
| DA-60 | IPI | 7.8 GB | 80 MB/s | 4+P RAID-3 | 80 MB/s |
| DA-62 | IPI | 10.9 GB | 32 MB/s | 4+P RAID-3 | 32 MB/s |
| DA-301 | IPI | 5.5 GB | 32 MB/s | 4+P RAID-3 | 32 MB/s |
| DA-302 | IPI | 7.2 GB | 37 MB/s | 4+P RAID-3 | 37 MB/s |
| DA-308 | Fibre Channel | 38 GB | 48 MB/s | 4+P RAID-3 | 240 MB/s |
| ND-40E | HIPPI | Up to 200 GB (per bank) |
186 MB/s | User definable RAID-1, -5 |
260 MB/s (4 banks) |
The DA-308 is the new disk array shipped on GigaRing systems. The Fibre Channel interface, although relatively new, has become the interface of choice for high-performance disks. The SCSI interface continues to be popular within the industry, but GigaRing SCSI disk products are not available in array configurations and therefore do not offer the performance and resiliency features that are available in the Fibre Channel disk subsystem. The Fibre Channel interface and the GigaRing Fibre Channel Node (FCN) will be the primary disk interface and controller through the year 2000 on GigaRing systems.
From an external view, the FCN appears similar to the IPI interface node. However, architecturally there are several differences related to Fibre Channel and new disk technology. The key differences can be outlined as follows:
The Fibre Channel interface is a serial interface that operates at approximately 1Gbit per second. Fibre Channel Arbitrated Loop protocol is used to connect many drives on the same loop and realize the bandwidth of many more drives than is possible with SCSI or IPI. The use of the serial array enables the FCN to run five arrays in parallel to achieve higher bandwidth. An good example of the advantage is comparing the GigaRing IPI RAID controller (IPN) to the FCN. The IPN with DD-60 drives can achieve 80 MB/s, whether connected to one or more arrays, but the FCN with five DA-308 arrays can achieve five times the single array bandwidth, or 240 MB/s.
The first Fibre Channel disks were shipped on GigaRing systems in April 1997. Only JBOD configurations were supported at that time. Fibre Channel RAID Software was released in a Beta release in October of 1997. This was followed by a production release in December 1997, which was SWS-ION 3.7. This first release delivered RAID functionality and the performance levels referred to in Table 3. In addition to the SWS-ION 3.7 release, mods were required in UNICOS or UNICOS/mk to support the alternate path feature and configuration and installation. UNICOS 10.0 and UNICOS/mk 2.0.0.50 included these mods. Additional bug fixes and a new disk drive micro-code were released in April 1998, which addressed issues with drive initialization and hot swap.
One hardware enhancement has been completed since first introduction of Fibre Channel disks: the capability to connect drives via fiber optic cables at lengths up to 300 meters. This feature will be available in the third quarter of 1998.
Work on software enhancements continues. Investigations into further optimizing use of buffers and queueing of requests have shown that additional performance can be achieved. These enhancements will be included in subsequent releases of SWS/ION.
The maximum measured performance levels of the Fibre Channel Node and IPI nodes are shown in Table 3 (CRInform version only). The table illustrates the point that the IPI GigaRing Node can utilize the bandwidth of a single array while the Fibre Channel Node can support the bandwidth of up to five arrays.
| Table 3 is available in the CRInform version of this paper. |
DD-309 disk drives will be introduced on Cray GigaRing systems in the third quarter of 1998. The product chosen as the follow-on to the DD-308 is the 10,000 RPM version of the 18GB disk drive (20 GB when formatted with 4K byte sectors). Table 4 shows the characteristics of the DD-309 disk drive.
DD-309s will be packaged in the DSF-2, a 3-Standard Unit 19" rack compatible chassis similar to the DSF-1 used on DD308s. Both copper and fiber optic cabling will be supported and can extend the distance from the FCN to DSF-2 to 300 meters.
In-house tests to fully characterize performance have not been completed. Preliminary single drive and array tests have been run and the performance numbers are shown in Table 5 (CRInform version only), with DD-308 numbers shown for comparison.
| Product | DD-308 | DD-309 |
|---|---|---|
| Capacity | 9.5 GB | 20 GB |
| RPM | 7200 | 10,000 |
| Transfer rate (outer zone) | 12 MB/s | 21 MB/s |
| Transfer rate (inner zone) | 7 MB/s | 14 MB/s |
| TPI | 5555 | 8962 |
| BPI (max) | 124,000 | 183,000 |
| Average seek time | 9.5 ms | 6.5 ms |
| Seek time, single track | 1.1 ms | 0.9 ms |
| Seek time, full stroke | <20 ms | <13 ms |
| Table 5 is available in the CRInform version of this paper. |
Fibre Channel disks and arrays have shown continual increases in performance since their introduction in 1997. These increases will continue with improvements in software and new disk devices at least through the year 2000. Table 6 (CRInform version only) shows the characteristics of the drives and subsystems of 1997, second half of 1998, and possible characteristics of year 2000 subsystems.
| Table 6 is available in the CRInform version of this paper. |