We have tested with the fastest hard disk at this time, the Samsung Spinpoint F1 with 32 MB cache. Our tests showed that this disc, without Raid, is capable of reaching sustained speeds of 105 MB / s for reading and 96 MB / s for writing (excluding cache), which is well above what other currently marketed SATA disks can achieve.
To highlight the disk performance, we used the SpeedTools Utilities and its software QuickBench 4, which has the merit of providing reliable and reproducible results.
We tested configurations RAID 0 with 2, 3 and 4 disks. To ensure that the system does not interfere with the tests, we started on a SATA disk installed in the unoccupied optical bay of our Mac Pro (machine in early 2008 to 3.2 GHz with 8 GB of RAM).
To begin, here are the results obtained by reading:
For starters, we can see the impact of cache, and the effect of a RAID disk array. the more the disks, the greater effect on the long rates, with a 16 KB with one disk to 50 MB disk with 4 (these enormous differences can be attributed to the fact that it did not have time to flush the buffers between two tests).
For writing, the effect of the cache is even more obvious. Obviously, a good part of it is because of cache..
In order to gain a clearer view on rates, we made a last test on a folder of 400 Mo. It has been repeated many times. We saved the best results:
Of course, the cache still has an impact, at least at the beginning of the copy. This effect is as important as increasing the number of disks.
But you can see that the RAID 0 software for Mac OS X is particularly well optimized and allows impressive data rates ,easily exceeding 400 MB / s reading and writing, to the delight of the video professionals, for 4TB Raid volumes
RAID 0, however, has an impact on other performances, such as access to very small files. This can be seen especially on reading tests in the first graph. The flow of reading files ofm less than 10 MB is slower with 4 discs than with 3. Because the RAID loses a little bit of time to go pick this information from 4 discs, and this time lost could not be caught up with the extra disk (one fetch across 3 disks gets the required data, adding a 4th disk just increasese the overhead).
Today, given the modus operandi of Mac OS X, the amateurs will be at ease with RAID 0 with 2 disks, which will make their machine fast and allow them to have other internal disks for backup . Indeed, RAID 0 increases the risk of losing data. If a single hard disk fails, everything is lost. We must therefore ensure even more safeguards.
Professionals will use a RAID 0 of 3 or 4 discs for specific needs that require significant very fast transfers.
Finally, we touch on the Apple RAID card. On paper it seemed ideal for all uses. However, we had such poor performance from it, we have appointed a member of the Team to test new Raid arrays on a different Mac Pro. Once it is completed and correlated with our current results, we will publish an article on RAID in a Mac Pro, citing these results but with further comments.
