[DRBD-user] Large block IO bottleneck

[Ross S. W. Walker]

Let me follow up on my own post by asking another question, maybe more
for the developers list, why is the max_sectors set to the PAGE_SIZE and
not the capabilities of the backing device? Will the driver not handle
the kind of throughput that a hardware based RAID card can generate? By
setting the max_sectors to 8 from the hardware's 128 severely limits
throughput (to 1/3 normal).

-Ross
 

> -----Original Message-----
> From: drbd-user-bounces at lists.linbit.com 
> [mailto:drbd-user-bounces at lists.linbit.com] On Behalf Of Ross 
> S. W. Walker
> Sent: Tuesday, January 02, 2007 4:05 PM
> To: drbd-user at lists.linbit.com
> Subject: [DRBD-user] Large block IO bottleneck
> 
> 
> Hi there I am using DRBD 0.7.21 with iSCSI Enterprise Target 0.4.14 on
> CentOS 4.4.
> 
> When I run iSCSI direct to the LVM lv on top of hardware RAID 
> I can get
> 225 MB/s over two sessions in MPIO with 256K block size, but 
> when I put
> DRBD in-between iSCSI and LVM the throughput tops out at 80 MB/s and I
> can't seem to go over that.
> 
> DRBD seems to report it's max number of sectors as 8 (4K), does that
> mean each io operation is limited to 4K? My hardware raid reports it's
> max sectors as 128, could this explain the reduction to 1/3 
> throughput?
> 
> 
> 
> Ross S. W. Walker
> Information Systems Manager
> Medallion Financial, Corp.
> 437 Madison Avenue
> 38th Floor
> New York, NY 10022
> Tel: (212) 328-2165
> Fax: (212) 328-2125
> WWW: http://www.medallion.com <http://www.medallion.com> 
> 
> 
> 
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