Sorry for the spam but I just noticed that the XFS stripe unit does not
match the strip unit of the underlying RAID device. I tried to do a
mkfs.xfs with a stripe of 512KiB but mkfs.xfs complains that the
maximum stripe width is 256KiB.
So I recreated the RAID with a stripe of 256KiB:
$ cat /proc/mdstat
Personalities : [linear] [raid6] [raid5] [raid4]
md0 : active raid5 sdc2[3] sdb2[1] sda2[0]
1932957184 blocks super 1.2 level 5, 256k chunk, algorithm 2 [3/2] [UU_]
resync=DELAYED
bitmap: 1/1 pages [4KB], 2097152KB chunk
and called mkf.xfs with proper parameters:
$ mkfs.xfs -d sunit=512,swidth=1024 -f -l size=32m /dev/md0
Unfortunately the file is still created unaligned to the RAID stripe.
$ xfs_bmap -vvp /tmp/diskmnt/filewr.zero
/tmp/diskmnt/filewr.zero:
EXT: FILE-OFFSET BLOCK-RANGE AG AG-OFFSET TOTAL FLAGS
0: [0..507903]: 2048544..2556447 0 (2048544..2556447) 507904 01111
FLAG Values:
010000 Unwritten preallocated extent
001000 Doesn't begin on stripe unit
000100 Doesn't end on stripe unit
000010 Doesn't begin on stripe width
000001 Doesn't end on stripe width
Now I'm out of ideas..
- Martin
On Thu, Nov 21, 2013 at 8:31 AM, Martin Boutin <martboutin@xxxxxxxxx> wrote:
> $ uname -a
> Linux haswell1 3.10.10 #1 SMP PREEMPT Wed Oct 2 11:22:22 CEST 2013
> i686 GNU/Linux
>
> $ xfs_repair -V
> xfs_repair version 3.1.4
>
> $ cat /proc/cpuinfo | grep processor
> processor : 0
> processor : 1
>
> $ mkfs.xfs -s size=4096 -f -l size=32m /dev/md0
> $ mount -t xfs /dev/md0 /tmp/diskmnt/
> $ dd if=/dev/zero of=/tmp/diskmnt/filewr.zero bs=1M count=1000 oflag=direct
> 1000+0 records in
> 1000+0 records out
> 1048576000 bytes (1.0 GB) copied, 28.0304 s, 37.4 MB/s
>
> $ cat /proc/meminfo
> MemTotal: 1313956 kB
> MemFree: 1099936 kB
> Buffers: 13232 kB
> Cached: 141452 kB
> SwapCached: 0 kB
> Active: 128960 kB
> Inactive: 55936 kB
> Active(anon): 30548 kB
> Inactive(anon): 1096 kB
> Active(file): 98412 kB
> Inactive(file): 54840 kB
> Unevictable: 0 kB
> Mlocked: 0 kB
> HighTotal: 626696 kB
> HighFree: 452472 kB
> LowTotal: 687260 kB
> LowFree: 647464 kB
> SwapTotal: 72256 kB
> SwapFree: 72256 kB
> Dirty: 8 kB
> Writeback: 0 kB
> AnonPages: 30172 kB
> Mapped: 15764 kB
> Shmem: 1432 kB
> Slab: 14720 kB
> SReclaimable: 6632 kB
> SUnreclaim: 8088 kB
> KernelStack: 1792 kB
> PageTables: 1176 kB
> NFS_Unstable: 0 kB
> Bounce: 0 kB
> WritebackTmp: 0 kB
> CommitLimit: 729232 kB
> Committed_AS: 734116 kB
> VmallocTotal: 327680 kB
> VmallocUsed: 10192 kB
> VmallocChunk: 294904 kB
> DirectMap4k: 12280 kB
> DirectMap4M: 692224 kB
>
> $ cat /proc/mounts
> (...)
> /dev/md0 /tmp/diskmnt xfs
> rw,relatime,attr2,inode64,sunit=1024,swidth=2048,noquota 0 0
>
> $ cat /proc/partitions
> major minor #blocks name
>
> 8 0 976762584 sda
> 8 1 10281600 sda1
> 8 2 966479960 sda2
> 8 16 976762584 sdb
> 8 17 10281600 sdb1
> 8 18 966479960 sdb2
> 8 32 976762584 sdc
> 8 33 10281600 sdc1
> 8 34 966479960 sdc2
> (...)
> 9 1 20560896 md1
> 9 0 1932956672 md0
>
> # same layout for other disks
> $ fdisk -c -u /dev/sda
>
> The device presents a logical sector size that is smaller than
> the physical sector size. Aligning to a physical sector (or optimal
> I/O) size boundary is recommended, or performance may be impacted.
>
> Command (m for help): p
>
> Disk /dev/sda: 1000.2 GB, 1000204886016 bytes
> 255 heads, 63 sectors/track, 121601 cylinders, total 1953525168 sectors
> Units = sectors of 1 * 512 = 512 bytes
> Sector size (logical/physical): 512 bytes / 4096 bytes
> I/O size (minimum/optimal): 4096 bytes / 4096 bytes
> Disk identifier: 0x00000000
>
> Device Boot Start End Blocks Id System
> /dev/sda1 2048 20565247 10281600 83 Linux
> /dev/sda2 20565248 1953525167 966479960 83 Linux
>
> # unfortunately I had to reinitelize the array and recovery takes a
> while.. it does not impact performance much though.
> $ cat /proc/mdstat
> Personalities : [linear] [raid6] [raid5] [raid4]
> md0 : active raid5 sda2[0] sdc2[3] sdb2[1]
> 1932956672 blocks super 1.2 level 5, 512k chunk, algorithm 2 [3/2] [UU_]
> [>....................] recovery = 2.4% (23588740/966478336)
> finish=156.6min speed=100343K/sec
> bitmap: 0/1 pages [0KB], 2097152KB chunk
>
>
> # sda sdb and sdc are the same model
> $ hdparm -I /dev/sda
>
> /dev/sda:
>
> ATA device, with non-removable media
> Model Number: HGST HCC541010A9E680
> (...)
> Firmware Revision: JA0OA560
> Transport: Serial, ATA8-AST, SATA 1.0a, SATA II
> Extensions, SATA Rev 2.5, SATA Rev 2.6; Revision: ATA8-AST T13 Project
> D1697 Revision 0b
> Standards:
> Used: unknown (minor revision code 0x0028)
> Supported: 8 7 6 5
> Likely used: 8
> Configuration:
> Logical max current
> cylinders 16383 16383
> heads 16 16
> sectors/track 63 63
> --
> CHS current addressable sectors: 16514064
> LBA user addressable sectors: 268435455
> LBA48 user addressable sectors: 1953525168
> Logical Sector size: 512 bytes
> Physical Sector size: 4096 bytes
> Logical Sector-0 offset: 0 bytes
> device size with M = 1024*1024: 953869 MBytes
> device size with M = 1000*1000: 1000204 MBytes (1000 GB)
> cache/buffer size = 8192 KBytes (type=DualPortCache)
> Form Factor: 2.5 inch
> Nominal Media Rotation Rate: 5400
> Capabilities:
> LBA, IORDY(can be disabled)
> Queue depth: 32
> Standby timer values: spec'd by Standard, no device specific minimum
> R/W multiple sector transfer: Max = 16 Current = 16
> Advanced power management level: 128
> DMA: mdma0 mdma1 mdma2 udma0 udma1 udma2 udma3 udma4 udma5 *udma6
> Cycle time: min=120ns recommended=120ns
> PIO: pio0 pio1 pio2 pio3 pio4
> Cycle time: no flow control=120ns IORDY flow control=120ns
>
> $ hdparm -I /dev/sd{a,b,c} | grep "Write cache"
> * Write cache
> * Write cache
> * Write cache
> # therefore write cache is enabled in all drives
>
> $ xfs_info /dev/md0
> meta-data=/dev/md0 isize=256 agcount=32, agsize=15101312 blks
> = sectsz=4096 attr=2
> data = bsize=4096 blocks=483239168, imaxpct=5
> = sunit=128 swidth=256 blks
> naming =version 2 bsize=4096 ascii-ci=0
> log =internal bsize=4096 blocks=8192, version=2
> = sectsz=4096 sunit=1 blks, lazy-count=1
> realtime =none extsz=4096 blocks=0, rtextents=0
>
> $ xfs_bmap -vvp /tmp/diskmnt/filewr.zero
> /tmp/diskmnt/filewr.zero:
> EXT: FILE-OFFSET BLOCK-RANGE AG AG-OFFSET TOTAL FLAGS
> 0: [0..2047999]: 2049056..4097055 0 (2049056..4097055) 2048000 01111
> FLAG Values:
> 010000 Unwritten preallocated extent
> 001000 Doesn't begin on stripe unit
> 000100 Doesn't end on stripe unit
> 000010 Doesn't begin on stripe width
> 000001 Doesn't end on stripe width
> # this does not look good, does it?
>
> # run while dd was executing, looks like we have almost the half
> writes as reads....
> $ iostat -d -k 30 2 /dev/sda2 /dev/sdb2 /dev/sdc2
> Linux 3.10.10 (haswell1) 11/21/2013 _i686_ (2 CPU)
>
> Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
> sda2 13.75 6639.52 232.17 78863819 2757731
> sdb2 13.74 6639.42 232.24 78862660 2758483
> sdc2 13.68 55.86 6813.67 663443 80932375
>
> Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
> sda2 78.27 11191.20 22556.07 335736 676682
> sdb2 78.30 11175.73 22589.13 335272 677674
> sdc2 78.30 5506.13 28258.47 165184 847754
>
> Thanks
> - Martin
>
> On Thu, Nov 21, 2013 at 4:50 AM, Martin Boutin <martboutin@xxxxxxxxx> wrote:
>> On Thu, Nov 21, 2013 at 4:26 AM, Dave Chinner <david@xxxxxxxxxxxxx> wrote:
>>> On Thu, Nov 21, 2013 at 04:11:41AM -0500, Martin Boutin wrote:
>>>> On Mon, Nov 18, 2013 at 7:57 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote:
>>>> > On Mon, Nov 18, 2013 at 12:28:21PM -0600, Eric Sandeen wrote:
>>>> >> On 11/18/13, 10:02 AM, Martin Boutin wrote:
>>>> >> > Dear list,
>>>> >> >
>>>> >> > I am writing about an apparent issue (or maybe it is normal, that's my
>>>> >> > question) regarding filesystem write speed in in a linux raid device.
>>>> >> > More specifically, I have linux-3.10.10 running in an Intel Haswell
>>>> >> > embedded system with 3 HDDs in a RAID-5 configuration.
>>>> >> > The hard disks have 4k physical sectors which are reported as 512
>>>> >> > logical size. I made sure the partitions underlying the raid device
>>>> >> > start at sector 2048.
>>>> >>
>>>> >> (fixed cc: to xfs list)
>>>> >>
>>>> >> > The RAID device has version 1.2 metadata and 4k (bytes) of data
>>>> >> > offset, therefore the data should also be 4k aligned. The raid chunk
>>>> >> > size is 512K.
>>>> >> >
>>>> >> > I have the md0 raid device formatted as ext3 with a 4k block size, and
>>>> >> > stride and stripes correctly chosen to match the raid chunk size, that
>>>> >> > is, stride=128,stripe-width=256.
>>>> >> >
>>>> >> > While I was working in a small university project, I just noticed that
>>>> >> > the write speeds when using a filesystem over raid are *much* slower
>>>> >> > than when writing directly to the raid device (or even compared to
>>>> >> > filesystem read speeds).
>>>> >> >
>>>> >> > The command line for measuring filesystem read and write speeds was:
>>>> >> >
>>>> >> > $ dd if=/tmp/diskmnt/filerd.zero of=/dev/null bs=1M count=1000 iflag=direct
>>>> >> > $ dd if=/dev/zero of=/tmp/diskmnt/filewr.zero bs=1M count=1000 oflag=direct
>>>> >> >
>>>> >> > The command line for measuring raw read and write speeds was:
>>>> >> >
>>>> >> > $ dd if=/dev/md0 of=/dev/null bs=1M count=1000 iflag=direct
>>>> >> > $ dd if=/dev/zero of=/dev/md0 bs=1M count=1000 oflag=direct
>>>> >> >
>>>> >> > Here are some speed measures using dd (an average of 20 runs).:
>>>> >> >
>>>> >> > device raw/fs mode speed (MB/s) slowdown (%)
>>>> >> > /dev/md0 raw read 207
>>>> >> > /dev/md0 raw write 209
>>>> >> > /dev/md1 raw read 214
>>>> >> > /dev/md1 raw write 212
>>>> >
>>>> > So, that's writing to the first 1GB of /dev/md0, and all the writes
>>>> > are going to be aligned to the MD stripe.
>>>> >
>>>> >> > /dev/md0 xfs read 188 9
>>>> >> > /dev/md0 xfs write 35 83o
>>>> >
>>>> > And these will not be written to the first 1GB of the block device
>>>> > but somewhere else. Most likely a region that hasn't otherwise been
>>>> > used, and so isn't going to be overwriting the same blocks like the
>>>> > /dev/md0 case is going to be. Perhaps there's some kind of stripe
>>>> > caching effect going on here? Was the md device fully initialised
>>>> > before you ran these tests?
>>>> >
>>>> >> >
>>>> >> > /dev/md1 ext3 read 199 7
>>>> >> > /dev/md1 ext3 write 36 83
>>>> >> >
>>>> >> > /dev/md0 ufs read 212 0
>>>> >> > /dev/md0 ufs write 53 75
>>>> >> >
>>>> >> > /dev/md0 ext2 read 202 2
>>>> >> > /dev/md0 ext2 write 34 84
>>>> >
>>>> > I suspect what you are seeing here is either the latency introduced
>>>> > by having to allocate blocks before issuing the IO, or the file
>>>> > layout due to allocation is not idea. Single threaded direct IO is
>>>> > latency bound, not bandwidth bound and, as such, is IO size
>>>> > sensitive. Allocation for direct IO is also IO size sensitive -
>>>> > there's typically an allocation per IO, so the more IO you have to
>>>> > do, the more allocation that occurs.
>>>>
>>>> I just did a few more tests, this time with ext4:
>>>>
>>>> device raw/fs mode speed (MB/s) slowdown (%)
>>>> /dev/md0 ext4 read 199 4%
>>>> /dev/md0 ext4 write 210 0%
>>>>
>>>> This time, no slowdown at all on ext4. I believe this is due to the
>>>> multiblock allocation feature of ext4 (I'm using O_DIRECT, so it
>>>> should be it). So I guess for the other filesystems, it was indeed
>>>> the latency introduced by block allocation.
>>>
>>> Except that XFS does extent based allocation as well, so that's not
>>> likely the reason. The fact that ext4 doesn't see a slowdown like
>>> every other filesystem really doesn't make a lot of sense to
>>> me, either from an IO dispatch point of view or an IO alignment
>>> point of view.
>>>
>>> Why? Because all the filesystems align identically to the underlying
>>> device and all should be doing 4k block aligned IO, and XFS has
>>> roughly the same allocation overhead for this workload as ext4.
>>> Did you retest XFS or any of the other filesystems directly after
>>> running the ext4 tests (i.e. confirm you are testing apples to
>>> apples)?
>>
>> Yes I did, the performance figures did not change for either XFS or ext3.
>>>
>>> What we need to determine why other filesystems are slow (and why
>>> ext4 is fast) is more information about your configuration and block
>>> traces showing what is happening at the IO level, like was requested
>>> in a previous email....
>>
>> Ok, I'm going to try coming up with meaningful data. Thanks.
>>>
>>> Cheers,
>>>
>>> Dave.
>>> --
>>> Dave Chinner
>>> david@xxxxxxxxxxxxx
>>
>>
>>
>> --
>> Martin Boutin
--
Martin Boutin
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