Seagate Savvio 10K.1 RAID

We have recently reviewed Seagate Savvio 10K.1 — the first 2.5-inch 10K storage drive, designed for compact high-performance servers and data storage systems. Small dimensions and weight, high capacitivity, reduced power consumption and heat dissipation, quieter operation, higher efficiency per occupied room, and many other aspects make these storage drives almost an ideal solution for blade servers, servers, and data storage systems in 1U format, high-performance 2U solutions, and other applications, where the compact dimensions are critical. Three models with the most popular professional interfaces promote the application flexibility of Seagate Savvio — Ultra320 SCSI, Fibre Channel 2 Gb/s, and Serial Attached SCSI (SAS).

As we have already noted, the appearance of Savvio-series storage drives (and products of the same format from other manufacturers) allows to review cardinally the approach to building compact servers (1U, blade) and data storage devices, offering a new quality for such systems, impossible without Savvio. Savvio can also significantly improve scalability of more traditional middle-sized data storage systems, though the main application of Savvio is still small-sized systems.

At the same time, we should note indifference of the majority of users to Savvio, — incomplete industrial infrastructure for storage drives of this format used to hamper the introduction of these extraordinary products into mass usage. Sales statistics prove that as well — the main Savvio consumers are just five largest IT companies from the USA. For example, these drives are not quite at home in Russia so far (though the ice is broken and these drives can already be found on the shelves without any special problems).

By force of application specifics (mostly small servers and data storage systems) Savvio storage drives are intended for RAIDs (however, a single Savvio drive can be used in a blade server) rather than single usage (performance of a single Savvio has been reviewed in the previous article, we found out a lot of interesting things). So it will be reasonable for us to test this aspect. At first (that is in this article), we shall connect them in pairs and analyze their performance in RAID 0 and 1. Anticipating questions like "why not RAID 5?", I note that Savvio's operation in simplest double-drive arrays is of practical interest and is frequently used in real life — one of the key applications for Savvii being blade servers, where you can hardly install more than two drives (even if that small).

A sample blade server with two Seagate Savvio storage drives.

Double-drive Savvio arrays are also used in some inexpensive 1U servers as well as for some special applications (for example, mobile servers and data storage systems), where weight and dimensions are critical. It's not difficult to draw conclusions on performance and 4-drive RAID 10 (they are more preferable in some cases than RAID 5, which require special high-performance controllers) based on test results of RAID 0 and RAID 1. So it seems quite logical to start analyzing RAID 0 and 1 performance of Savvio drives. We'll try to get back to RAID 5 on these storage drives later, probably on a different testbed — using SAS storage drives and controllers. Which is quite logical in terms of market prospects for these drives.

As we have analyzed Savvio 10K.1 characteristics in the previous article, we are going to proceed right to the tests.

Test participants and methods of testing performance

We used two Seagate Savvio 10K.1 ST973401LC 73.4 GB drives with initial firmware 0001 as well as two Seagate Cheetah 10K.7 drives of the same capacity. Performance of double-drive RAIDs 0 and 1 was compared between each other and the results of single storage drives. Besides, we used a single Seagate Cheetah 15K.4 147 GB with the spindle rotational speed of 15000 rpm, in order to determine how well simple RAIDs based on 10K models can compete with the fastest 15K storage drives. All Seagate storage drives were tested in Server Mode (PM=off).

We used the following testbed configuration to test storage drives:

• CPU: Intel Pentium 4 3.0C
• Gigabyte GA-8KNXP Ultra-64 motherboard based on Intel E7210 chipset (the i875P with Hance Rapids 6300ESB southbridge and PCI-X bus)
• RAM: 2x256 MB DDR400 (2.5-3-3-6 timings)
• Ultra320 SCSI Adaptec AIC-7902B controller on PCI64 bus
• The main hard drive: Maxtor 6E040L0
• Power supply: Zalman ZM400A-APF, 400W
• Chassis: Arbyte YY-W201BK-A

This motherboard was chosen on purpose. Firstly, Intel E7210 chipset is intended for workstations and single-processor low end servers based on Pentium 4 and Xeon (which conforms well with the application area of single and doubled SCSI drives of this class), though it will do well for desktop systems (because it's based on the i875P). Secondly, this professional system contains a fully functional (with some reservations though) PCI-X bus (as well as PCI64), provided directly by the chipset (instead of additional bridges). Thirdly, this motherboard houses a good dual-channel Ultra320 SCSI RAID controller — Adaptec AIC-7902B, connected to PCI64 bus,

RAID controller Adaptec AIC-7902W based on PCI64 base on Gigabyte GA-8KNXP Ultra-64 motherboard.

which fits our purposes much better (testing hard drives proper and simple RAIDs) than a more expensive one with onboard memory, because Adaptec seems the most popular (at least in our country) brand of SCSI controllers. No additional memory in this controller allows to measure HDD performance in the "purest" form, unaffected by possible caching of the controller and its data stream processing algorithms.

All SCSI models were tested as single storage drives (and demonstrated similar results) as well as part of RAIDs 1 and 0 (in the latter case, the block size is 256 KB by default). That's how this RAID and the controller look like in Device Manager under Windows XP:

The controller (in non-RAID mode) uses Adaptec driver 3.0.0.0 dated September 2004, in case of RAID we used driver 3.0.36.0 dated July 2004. The tests were carried out under MS Windows XP Professional SP2. The hard disks were tested not partitioned (in Intel Iometer 2003.5.10, H2Benchw 3.6 and AIDA5 tests) as well as partitioned and formatted by regular operating system tools depending on a test type: one NTFS partition of maximum size for testing the average access time and plotting the read rate graph in WinBench 99 and two NTFS or FAT32 partitions of the same size for other tests (WinBench Disk WinMark 99 2.0, ATTO Disk Benchmark test, multithreaded read/write, and the Adobe Photoshop CS test). Each NTFS partition occupied half of the entire disk capacity (that is the second partition started exactly from the second half of the disk). FAT32 partitions were 32768MB, the first one starting at the outer edge of the media (on the "fastest" tracks), and the second — exactly from the middle of the media volume. NTFS and FAT32 cluster sizes were selected by default — 4 and 16 KB correspondingly

The storage drives were mounted firmly on the metal chassis of the PC case and blown over by small face fans for a 5-inch bay. They were warmed up for 20 minutes before the test using a program with active random access.

Results of the physical parameter tests

Linear reading rate graphs are the first to go (click icons to see full-sized graphs).

There is nothing unexpected here — the RAID 1 graph is a perfect match to the single-drive graph, RAID 0 demonstrates twice as high performance and capacity. Double-drive RAIDs on Cheetah 10K.7 are much faster in transfer rates, but a simple RAID 0 on Savvio 10K.1 takes up less room and possesses much higher transfer rates than a single Cheetah 15K.4 (besides, its power consumption is much lower).

Ultra320 SCSI interface rate is practically the same in all cases (a small performance drop in RAID 0 is insignificant).

Using other approaches to measure bus transfer rates allows to squeeze maximum 210-240 MB/s, which is not quite bad.

What concerns the average access time for reading in double-drive RAIDs, while Cheetah 10K.7 shows no difference from a single storage drive, Savvio demonstrates a minor improvement in RAID 1 and especially in RAID 0 — its access time improved by 0.1-0.2 ms. But alas, these raids are still outclassed by the high-performance seek in Cheetah 15K.4.

Both RAIDs 0 demonstrate a twofold reduction of the effective write access time compared to RAID 1 (it's quite easy to understand, considering random access and disk striping in Array Level 0). On the other hand, while RAID 1 on Cheetah 10K.7 offers the same access time for writing as the single storage drive (it's only natural), the write access time in Savvio array got noticeably worse!

It cannot be written off to test drawbacks, as the situation repeats itself in independent measurements in Intel IOMeter. However, I see no catastrophe in it, as the write access time in RAID 1 on Savvio remains on the level of RAID 1 on Cheetah 10K.7.