Hi Stan,
Thanks for the long email (I didn't know about advance formatting for
one) - please see my answers inline.
On 30/12/2013 19:56, Stan Hoeppner wrote:
On 12/29/2013 3:04 PM, Pieter De Wit wrote:
<snip>
So my question is, do I need to align the partitions for the raid devices ?
<snip>
Are these 2TB Advanced Format drives? If so your partitions need to
align to 4KiB boundaries, otherwise you'll have RMW within each drive
which can cut your write throughput by 30-50%.
Yes - these drives are, parted printed:
Model: ATA WDC WD20EARX-008 (scsi)
Disk /dev/sdb: 3907029168s
Sector size (logical/physical): 512B/4096B
Partition Table: gpt
Number Start End Size File system Name Flags
1 2048s 500000767s 499998720s raid
2 500000768s 3907028991s 3407028224s raid
<snip>
So given your comments then, the start of partition 1 is correct. The
start of partition 2 is also correct (not sure if this is needed), but
the size of partition 2 is incorrect, it should be 3406823424s ?
You're comparing apples to oranges to grapes below, and your description
lacks any level of technical detail. How are we supposed to analyze this?
These are desktop grade drives, but for the RAID0 device I saw quite low
throughput (15meg/sec moving data to the NAS via gig connection). I just
"15meg/sec moving data" means what, a bulk file transfer from a local
filesystem to a remote filesystem? What types of files? Lots of small
ones? Of course throughput will be low. Is the local filesystem
fragmented? Even slower.
It's all done with pvmove, which moves 4meg chunks
created a RAID1 device between /dev/sda and an iSCSI target on the NAS,
and it synced at 48meg/sec, moving data at 30meg/sec - double that of
the RAID0 device.
This is block device data movement. There is no filesystem overhead, no
fragmentation causing excess seeks, and no NFS/CIFS overhead on either
end. Of course it will be faster.
It was all done with pvmove :)
I would have expected the RAID0 device to easily get
up to the 60meg/sec mark ?
As the source disk of a bulk file copy over NFS/CIFS? As a point of
reference, I have a workstation that maxes 50MB/s FTP and only 24MB/s
CIFS to/from a server. Both hosts have far in excess of 100MB/s disk
throughput. The 50MB/s limitation is due to the cheap Realtek mobo NIC,
and the 24MB/s is a Samba limit. I've spent dozens of hours attempting
to tweak Samba to greater throughput but it simply isn't capable on that
machine.
Your throughput issues are with your network, not your RAID. Learn and
use FIO to see what your RAID/disks can do. For now a really simple
test is to time cat of a large file and pipe to /dev/null. Divide the
file size by the elapsed time. Or simply do a large read with dd. This
will be much more informative than "moving data to a NAS", where your
throughput is network limited, not disk.
The system is using a server grade NIC, I will run a dd/network test
shortly after the copy is done. (I am shifting all the data back to the
NAS, incase I mucked up the partitions :) ), I do recall that this
system was able to fill a gig pipe...
Thanks,
Pieter
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
