Re: File system performance, hardware performance, ext3, 3ware RAID1, etc.
From: Willy Tarreau (willy_at_w.ods.org)
Date: 02/13/04
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Date: Fri, 13 Feb 2004 06:53:50 +0100 To: Timothy Miller <miller@techsource.com>
On Thu, Feb 12, 2004 at 06:32:31PM -0500, Timothy Miller wrote:
> For writes, iozone found an upper bound of about 10megs/sec, which is
> abysmal. Typically, I'd expect writes to be faster (on a single drive)
> than reads, because once the write is sent, you can forget about it.
> You don't have to wait around for something to come back, and that
> latency for reads can hurt performance. The OS can also buffer writes
> and reorder them in order to improve efficiency.
It depends on the disk too. Lots of disks (specially IDE) are far slower
on writes than they are on reads.
> The 3ware has this write cache that you can turn on or off. With it
> off, it ensures that writes make it to the disks in order. With it on,
> it will reorder writes more efficiently. However, I noticed that the
> performance only went up to about 16meg/sec with the cache ON.
I don't think that the FS type has much importance once the cache is ON.
> IMPORTANT QUESTION: Is there any metadata anywhere in the swap
> partition (when it's not in use) that I need to save before I fill it
> with zeros?
No, there's nothing to save, but you'll have to rebuild the swap at the
end of your tests : mkswap /dev/sga3
I too often use the swap partition for testing purpose or for temporary
storage ; it's easy to do a swapoff; mke2fs on it :-)
> Also, what do I use as a source for zeros when writing with dd?
> "/dev/zero"?
yes. but don't try to copy any file from the disk onto this partition,
because head seeks will slow things down.
> What's the command? How about this:
> time dd if=/dev/zero of=/dev/sga3 bs=1024 count=1024
do it like this, but use higher values, particularly for bs which is only
1kB here. Using something like bs=65536 and count=4096 will give you a 256 MB
file.
> Will that do it? Should I use an offset to avoid any kind of header or
> metadata?
not needed. Just ensure that you write to the right partition, and better
check twice.
Regards
Willy
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- Previous message: Con Kolivas: "[ANNOUNCE] kernbench-0.20"
- In reply to: Timothy Miller: "File system performance, hardware performance, ext3, 3ware RAID1, etc."
- Next in thread: Timothy Miller: "Re: File system performance, hardware performance, ext3, 3ware RAID1, etc."
- Reply: Timothy Miller: "Re: File system performance, hardware performance, ext3, 3ware RAID1, etc."
- Reply: Eric D. Mudama: "Re: File system performance, hardware performance, ext3, 3ware RAID1, etc."
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