From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pieter De Wit Subject: Re: Is partition alignment needed for RAID partitions ? Date: Mon, 30 Dec 2013 21:32:11 +1300 Message-ID: <52C12F8B.6080507@insync.za.net> References: <52C08E63.8020800@insync.za.net> <52C11929.3070600@hardwarefreak.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <52C11929.3070600@hardwarefreak.com> Sender: linux-raid-owner@vger.kernel.org To: stan@hardwarefreak.com, linux-raid List-Id: linux-raid.ids 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: >> >> So my question is, do I need to align the partitions for the raid devices ? > > 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 > 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