$ 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
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