On Mon, 10 Mar 2003, Jesse Keating wrote: >>> # grep USE_DMA /etc/sysconfig/harddisks >>> USE_DMA=1 >>> >>> # hdparm -t /dev/hdb >>> /dev/hdb: >>> Timing buffered disk reads: 64 MB in 1.18 seconds = 54.07 MB/sec >>> >>This is different. It's setting an approved config file, for Red Hat init >>scripts to parse, and set hdparm options. It is not using hdparm directly on >>the disk. Some hdparm settings you can use, w/ little fear of data >>corruption. Some you can't. This is most likely what Arjan was referring >>to. Arjan's statements were pretty vague, so take them as that unless he >>clarifies a bit. > >I can clarify Arjan's statements a bit. Basically, in all modern >kernels, the kernel autodetects the hard disk's capabilities >itself, and sets the drive for the best performance >_automatically_ itself without any end user intervention. If for >any reason, a hard disk setting is _not_ enabled by the kernel, >it is because the kernel knows that that setting is not safe to >use. Or, as is the case with some versions of the kernel running on a motherboard with the E7500 chipset, the kernel just did not have a clue as to what the right thing to do was. To simply say the kernel knows best is not the right answer; it depends greatly on the circumstance, and how much time you have to invest. For an OEM, chances are the right answer is to look at the kernel code and verify the it is doing the right thing. If its not, try using the various hdparm settings in your lab and test the results. On the other hand if you are working with a production system, its probably not a good idea to mess with hdparm. The bottom line is that the kernel does not always know what is best, but its certainly best when it does...james
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