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. The kernel contains various blacklists/whitelists of known bad/good hardware combinations, known motherboard chipset bugs, and whatnot, and it sets the drive to enable the fastest transfer rates for your hardware combination that is also "safe" to use. If someone then goes and plays with hdparm settings, they may in fact be force-overriding the kernel's safety mechanisms, and enabling some setting that triggers a flaw in the drive, the motherboard chipset, or some combination of the two, and that may cause data corruption. Second guessing the hard disk settings that modern kernels default the drives to is Russian Roulette. Some settings might turn out to be harmless (or perhaps the kernel just ignores them and you _think_ the change did something), while other settings perhaps do change something (but have zero real effect on speed). Short Answer: Trust the kernel to do the right thing. -- Mike A. Harris ftp://people.redhat.com/mharris OS Systems Engineer - XFree86 maintainer - Red Hat -- Phoebe-list mailing list [EMAIL PROTECTED] https://listman.redhat.com/mailman/listinfo/phoebe-list
