Re: SATA-performance: Linux vs. FreeBSD

Martin A. Fink
2007-02-13T12:32:39Z

Am Dienstag, 13. Februar 2007 12:25 schrieben Sie:
> > Well they do. The Flash disk I have (SATA-I) is capable of 48 MB/s and
this
> > value is reached over the whole disk size by windows as well as by
FreeBSD.
> > See my test results in the first thread.
>
> Ok a flash disk should be more stable
>
> > My Seagate Barracuda Harddisk drive (SATA-II) starts with 76 MB/s and
> > decreases linearly to 35 MB/s due to the fact that it has to write to a
> > rotating disk. But on a flash disk there is nothing rotating...
>
> The hard disk one isn't guaranteed or stable but the flash especially if
> it is aimed at it ought to behave.
>
> > So where is the difference between SATA-I and SATA-II ?
>
> All physical side if they are on the same controller when you do the
> tests. Mostly latency,
>
> > And why is FreeBSD able to write with constant rates (the complete 25 GB,
all
> > with 48+/-0.1 MB/s) but Linux 2.6.18 not ?
>
> Does the FreeBSD fsync sync to media ? Also what controller is being used
> here, and do you have EHCI USB support running ?
Manual of FreeBSD fsync says it syncs to media.

I used the same controller: Same computer, same harddisk. two partitions on
the system disk, one for linux, one for freebsd.

EHCI:

ehci_hcd 0000:00:1d.7: EHCI Host Controller
ehci_hcd 0000:00:1d.7: USB 2.0 started, EHCI 1.00, driver 10 Dec 2004
usb usb1: Product: EHCI Host Controller

AHCI

ahci 0000:00:1f.2: AHCI 0001.0100 32 slots 4 ports 3 Gbps 0xf impl SATA mode

>
> > With a dedicated (rotating) SATA II device, using the first 70% of disk
space
> > no problem -- tested ! With a SATA-I device only a problem with Linux
2.6.18
>
> I suspect the SATA-1 itself may not be the decider but something else -
> eg the hard disk using NCQ, which would cover up any latency related
> problems.
>
> > Journaling of data: you are right, ext2 performs better than ext3.
>
> And ext3 in writeback mode ought in theory (but practice is always
> harder ;)) be faster than ext2.
>
>

--
Dipl. Physiker
Martin Anton Fink
Max Planck Institute for extraterrestrial Physics
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85741 Garching
Germany
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