![]() | ||||||||||
Messages in this thread |
Eyal Lebedinsky wrote: > Nuno Silva wrote: >>Hi, >>Eyal Lebedinsky wrote: >>>I noticed that my 3-disk RAID was syncing at about 40MB/s, now that I >>>added a fourth disk it goes at only 20+MB/s. This is on an idle machine. >>3*40=120 >>4*20=80 > What does this mean? The raid is syncing at 20MB/s, not each disk, so I do > not see what the multiplication is about. Yes, you're correct :-) >>>Individually, each disk measures 60+MB/s with hdparm. >>And concurrent hdparms? Or some dd's concurrently? > > I do not see this as relevant, but four concurrent hdparms (each to a > different disk) give about 30MB/s per disk. I expect the controller > to talk to the four disks at their full speed so concurrency should > not be the issue. I guess you're using linux's software raid? If so, you're hitting the 120MB/sec (and I *think* this time I'm correct! :-) If this is a PCI32/33mhz slot you're not going to be able to get more juice. (I bet that 3 concurrent dd's gets you 40MB each). Anyway, this may be offtopic because the problem (only 20MB/sec for the raid with 4 disks) should be something else... Sorry for the noise. >>>kernel: 2.6.13 on ia32 >>>Controller: Promise SATAII150 TX4 >>>Disks: WD 320GB SATA >>> >>>Q: Is this the way the raid code works? The way the disk-io is >>>managed? Or >>>could it be due to the SATA controller? >> >>You can isolate the performance drop with some dd's. Maybe this card is >>in a pci32/33mhz and you're hitting the pci bus' limits? (120~130MB/sec). > > > 'hdparm -T' gives about 1250 MB/sec so this is not the limiting > factor. Mine outputs some fabulous values too... I'm not sure I trust them ;) # hdparm -T /dev/sda /dev/sda: Timing cached reads: 3536 MB in 2.00 seconds = 1767.38 MB/sec Regards, Nuno Silva - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | |||||||||
| Last update: 2005-09-10 06:54 [from the cache] ©2003-2008 | ||||||||||