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Hitachi Deskstar 7K400 and 7K250 HDD


Results of the physical parameter tests

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




First of all I want to note that we noticed no such negative effects as "noisy" and "floating" graphs in the 7K400 and 7K250 series disks as we previously came across in the senior 180GXP model. Despite the more capacious 80 GB platters, designers obtained steadier "data reception" by HDD heads. :) Hitachi still uses the "traditional" approach to platter formatting, though in its future desktop series we can expect so-called "adaptive" platter formatting, which has been long used in mobile storage devices from this company in order to increase the data density (up to 70 Gbit per inch2 versus 62 Gbit in desktop hard disks of the same generation) and reliability.

Hard disk graphs (in terms of one platter) practically match within each series (7K400 and 7K250), but inter-series graphs are somewhat different. Firstly, by the number and layout of formatting zones: I have visually counted 19 distinctive zones in 7K400 and 24 zones for 7K250 (the specifications claim 29 and 30 zones respectively). Secondly, formatting zones in 7K400 and 7K250 models are obviously different almost across the entire platter area. This difference is the most prominent in the first (the fastest) two thirds of the disk, where the zones in the 7K250 are located "higher" in general (i.e. read/write speed is obviously higher), and one can note that the zones in different hard disk series match only in the last third of the platters.

The latter effect is also demonstrated in the following: while the 7K400 hard disks slightly (homoeopathically) outscore the 7K250 series in maximum (in the very beginning of the media) linear read speed, the predecessors are noticeably faster (by 3%) than the novices in the average read speed, see the diagram below. And, for example, the 7K250 is faster than the novices by 10% in the middle of the media! The 7K400 is a tad slower than the old guys in its minimum speed as well.

IBM/Hitachi hard disks have always been very fast in interface data rate (UltraATA or Serial ATA). There is practically no gap between the models and series here, while SATA disks are approximately 20% faster in interface data rate than their UltraATA/100 counterparts. However, with their 8 MB buffer this difference will hardly be the determining factor in terms of disk performance in applications.

The senior SATA model from the 7K250 series turned out the fastest by its real average access time — just 12 ms, which is noticeably better than in its competitors (from other manufacturers). Though, to be just, I want to note that even 7K400 models with quite heavy blocks of 10 heads were only miserably outscored by the leader and leave behind most competitors as well as the six-head hard disk of the previous generation — IBM 180GXP.

As you may have already guessed, all modern desktop Hitachi hard disks support seek acoustics control via the Acoustics Management register. Acoustics in 7K400 and 7K250 series models was set to disabled (register value — 255dec) by default and the hard disks are rather noisy in active seek mode — especially 7K400 models! However, you can considerably reduce the seek noise by modifying (for example, using Hitachi Feature Tool) the value of this register to 128dec (or any other value, which is less than 192dec). This will increase the average access time approximately by 4 ms — up to a little over 16 ms. In this review we tested a 7K400 SATA model both in normal and in quiet slow seek modes, to understand how much performance is lost to quiet operation.

Additional information is provided by the comparison of the average access time measured separately for reading and writing — we may try to evaluate the efficiency of lazy write procedures and caching of written data in the buffer by how much the average access time drops in writing compared to reading.

Here we can see noticeable firmware differences between Hitachi hard disks of different series! Firstly, this index is very ineffective for 180GXP series hard disks (especially for these days) — it lags behind very much from Hitachi drives in "writing"! Secondly, SATA models slightly outscore UATA models in writing in all aspects — buffer fill rate over a faster interface has its effect. Thirdly, 7K250 series hard disks demonstrate obviously better write access index (that is lazy write) than newer 7K400 models. And finally, when the 7K400 is in quiet seek mode, its average write access time improves noticeably!!! This may warrant the assumption that lazy write procedures in this mode may change to more effective ones! (I already came up with this assumption before in the review of Hitachi Travelstar 7K60, though there were fewer reasons for this conclusion at that time than I have now.)

Alex Karabuto (lx@ixbt.com)
January 18, 2005

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