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boa
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 Posted: Fri Sep 22, 2006 8:06 pm Post subject: SCSI + Windows: Disappointing write performance? |
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Hi,
I've written a tiny program which just writes 2GB of data to disk,
nothing more. Running the program, writing to different disks and
configurations, leaves me a bit puzzled. My old&slow IDE drive is faster
than a 4-drive RAID-10 using brand new 15K SAS drives we just got. That
can't be right, can it?
The program seems to be CPU bound, not IO bound, consuming 100% of one
CPU on a quad PowerEdge 2850. All drivers and all firmware is upgraded
to latest version available.
Hardware on one of the servers I tested this on, a Quad Dell PowerEdge
2850, running W2003:
a) PERC5 RAID controller (PCI Express) + 4 15.000 RPM SAS drives
configured as RAID-10, cache write back is enabled. Duration 1:07
b) PERC4 RAID controller + 2 10.000 RPM U320 SCSI drives configured as
RAID-0, cache write back is enabled. Duration 1:10
c) Dell PowerEdge 2850 with PERC4 + 6 10.000 RPM U320 SCSI drives
configured as RAID-5, cache write back is enabled. Duration 2:05. (Not a
big surprise...)
And on my home PC, Intel Prescott 3.2GHz+WinXP Home, with one 10.000 RPM
S-ATA drive: 0:46
I also have a Linux box with a slow CPU(around 1.6GHz AMD something) and
a slow IDE disk (max 7200 RPM) using reiserfs: 1:02 minutes.
Compiler(on all platforms): GCC. (Gcc turned out to be faster than MS
Visual C++ 2005 on XP)
Any ideas? (Except switching to Unix? Hehe)
Boa |
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Eric Gisin
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| Posted: Fri Sep 22, 2006 11:01 pm Post subject: Re: SCSI + Windows: Disappointing write performance? |
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Did you CreateFile with unbuffered IO and page align the buffer (64KB or more)?
You can also try RAID 1 on the adapter with RAID 0 in Win XP.
"boa" <boasema@gmail.com> wrote in message news:S4mdndzjeNiWYY7YnZ2dnUVZ_76dnZ2d@telenor.com...
| Quote: | Hi,
I've written a tiny program which just writes 2GB of data to disk, nothing more. Running the
program, writing to different disks and configurations, leaves me a bit puzzled. My old&slow IDE
drive is faster than a 4-drive RAID-10 using brand new 15K SAS drives we just got. That can't be
right, can it?
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boa
Guest
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| Posted: Sat Sep 23, 2006 1:24 pm Post subject: Re: SCSI + Windows: Disappointing write performance? |
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* Eric Gisin wrote, On 22.09.2006 19:01:
| Quote: | Did you CreateFile with unbuffered IO and page align the buffer (64KB or more)?
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Nope, plain old ANSI C, using fopen() and fwrite().
Here's my 'theory':
1. The number of syscalls are the same regardless of target disk types.
2. No calls to fwrite() fail, as the file written to is 2GB on all disks.
3. Four 15K SAS drives in RAID-10 has to be faster than a 7.2K IDE.
So my best guess is that the Windows code for handling LVM is a lot
slower than the corresponding IDE code.
Boa
| Quote: | You can also try RAID 1 on the adapter with RAID 0 in Win XP.
"boa" <boasema@gmail.com> wrote in message news:S4mdndzjeNiWYY7YnZ2dnUVZ_76dnZ2d@telenor.com...
Hi,
I've written a tiny program which just writes 2GB of data to disk, nothing more. Running the
program, writing to different disks and configurations, leaves me a bit puzzled. My old&slow IDE
drive is faster than a 4-drive RAID-10 using brand new 15K SAS drives we just got. That can't be
right, can it?
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Mike Walsh
Guest
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| Posted: Sat Sep 23, 2006 7:04 pm Post subject: Re: SCSI + Windows: Disappointing write performance? |
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If I recall correctly there are some conditions where WinXP performance will be poor because it turns off write cache.
boa wrote:
| Quote: |
* Eric Gisin wrote, On 22.09.2006 19:01:
Did you CreateFile with unbuffered IO and page align the buffer (64KB or more)?
Nope, plain old ANSI C, using fopen() and fwrite().
Here's my 'theory':
1. The number of syscalls are the same regardless of target disk types.
2. No calls to fwrite() fail, as the file written to is 2GB on all disks.
3. Four 15K SAS drives in RAID-10 has to be faster than a 7.2K IDE.
So my best guess is that the Windows code for handling LVM is a lot
slower than the corresponding IDE code.
Boa
You can also try RAID 1 on the adapter with RAID 0 in Win XP.
"boa" <boasema@gmail.com> wrote in message news:S4mdndzjeNiWYY7YnZ2dnUVZ_76dnZ2d@telenor.com...
Hi,
I've written a tiny program which just writes 2GB of data to disk, nothing more. Running the
program, writing to different disks and configurations, leaves me a bit puzzled. My old&slow IDE
drive is faster than a 4-drive RAID-10 using brand new 15K SAS drives we just got. That can't be
right, can it?
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Mike Walsh
West Palm Beach, Florida, U.S.A. |
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boa
Guest
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| Posted: Sat Sep 23, 2006 11:33 pm Post subject: Re: SCSI + Windows: Disappointing write performance? |
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* Mike Walsh wrote, On 23.09.2006 15:04:
| Quote: | If I recall correctly there are some conditions where WinXP performance will be poor because it turns off write cache.
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OK, thanks. You don't by any chance recall the conditions and/or a
remedy? ;-)
BTW, XP was my fastest platform, but maybe this applies to W2003 server
as well?
Boa
| Quote: |
boa wrote:
* Eric Gisin wrote, On 22.09.2006 19:01:
Did you CreateFile with unbuffered IO and page align the buffer (64KB or more)?
Nope, plain old ANSI C, using fopen() and fwrite().
Here's my 'theory':
1. The number of syscalls are the same regardless of target disk types.
2. No calls to fwrite() fail, as the file written to is 2GB on all disks.
3. Four 15K SAS drives in RAID-10 has to be faster than a 7.2K IDE.
So my best guess is that the Windows code for handling LVM is a lot
slower than the corresponding IDE code.
Boa
You can also try RAID 1 on the adapter with RAID 0 in Win XP.
"boa" <boasema@gmail.com> wrote in message news:S4mdndzjeNiWYY7YnZ2dnUVZ_76dnZ2d@telenor.com...
Hi,
I've written a tiny program which just writes 2GB of data to disk, nothing more. Running the
program, writing to different disks and configurations, leaves me a bit puzzled. My old&slow IDE
drive is faster than a 4-drive RAID-10 using brand new 15K SAS drives we just got. That can't be
right, can it?
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Mike Walsh
Guest
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| Posted: Sun Sep 24, 2006 8:37 pm Post subject: Re: SCSI + Windows: Disappointing write performance? |
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I don't have any first hand knowledge of the problem, but I recall reading about it soon after WinXP was released when many people complained about SCSI performance. At some times windows would override your settings and disabled write cache on SCSI drives. Microsoft said this was a "feature" and was not limited to WinXP. I don't recall hearing about any fix for it. The only way I know to completely avoid the problem is to use ATA drives whose write cache can't be disabled.
boa wrote:
| Quote: |
* Mike Walsh wrote, On 23.09.2006 15:04:
If I recall correctly there are some conditions where WinXP performance will be poor because it turns off write cache.
OK, thanks. You don't by any chance recall the conditions and/or a
remedy? ;-)
BTW, XP was my fastest platform, but maybe this applies to W2003 server
as well?
Boa
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Mike Walsh
West Palm Beach, Florida, U.S.A. |
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