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Date: Mon, 08 Mar 2010 21:17:03 +0100
From: Paul Chavent <paul.chavent@...c.net>
To: tytso@....edu
CC: linux-ext4@...r.kernel.org
Subject: Re: Constant access (write) time.
Hello.
Thank you for your reply.
I have an intel SSD 2.5 inch X25-M 80GB SATA300. And i have the following log :
# /test_ext4
file size duration
58157568 11809470
62773248 10658968
266786304 11514789
287403008 10423548
308327424 13095972
329251840 11036123
350176256 12643903
370792960 9767548
391717376 10987771
411410944 13204409
^C
diff min : 2298627
diff moy : 3971804
diff max : 13204409
1342 iterations
major pagefaults : 0
minor pagefaults : 0
Could you give me more detail on your configuration ?
Here, more details on mine :
# mke2fs -t ext4 -L DATA -O large_file,^has_journal,extent -v /dev/sda3
mke2fs 1.41.9 (22-Aug-2009)
fs_types for mke2fs.conf resolution: 'ext4', 'default'
Filesystem label=DATA
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
3670016 inodes, 14653288 blocks
732664 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=0
448 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
4096000, 7962624, 11239424
Writing inode tables: done
Writing superblocks and filesystem accounting information: done
This filesystem will be automatically checked every 37 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.
# dumpe2fs -h /dev/sda3
dumpe2fs 1.41.9 (22-Aug-2009)
Filesystem volume name: DATA
Last mounted on: <not available>
Filesystem UUID: 13b72368-2a9e-11df-8a9f-0060c2140392
Filesystem magic number: 0xEF53
Filesystem revision #: 1 (dynamic)
Filesystem features: ext_attr resize_inode dir_index filetype extent flex_bg sparse_super large_file huge_file uninit_bg dir_nlink extra_isize
Filesystem flags: signed_directory_hash
Default mount options: (none)
Filesystem state: clean
Errors behavior: Continue
Filesystem OS type: Linux
Inode count: 3670016
Block count: 14653288
Reserved block count: 732664
Free blocks: 14409685
Free inodes: 3670005
First block: 0
Block size: 4096
Fragment size: 4096
Reserved GDT blocks: 1020
Blocks per group: 32768
Fragments per group: 32768
Inodes per group: 8192
Inode blocks per group: 512
Flex block group size: 16
Filesystem created: Mon Mar 8 10:33:46 2010
Last mount time: n/a
Last write time: Mon Mar 8 10:34:00 2010
Mount count: 0
Maximum mount count: 37
Last checked: Mon Mar 8 10:33:46 2010
Check interval: 15552000 (6 months)
Next check after: Sat Sep 4 10:33:46 2010
Lifetime writes: 900 MB
Reserved blocks uid: 0 (user root)
Reserved blocks gid: 0 (group root)
First inode: 11
Inode size: 256
Required extra isize: 28
Desired extra isize: 28
Default directory hash: half_md4
Directory Hash Seed: 13b723f4-2a9e-11df-8a9f-0060c2140392
# mount -t ext4 -o noatime,nodiratime /dev/sda3 /var/data
EXT4-fs (sda3): no journal
EXT4-fs (sda3): delayed allocation enabled
EXT4-fs: file extents enabled
EXT4-fs: mballoc enabled
EXT4-fs (sda3): mounted filesystem without journal
# hdparm -i /dev/sda
/dev/sda:
hdparm: ioctl 0x304 failed: Inappropriate ioctl for device
Model=INTEL SSDSA2MH080G1GC , FwRev=045C8820, SerialNo=CVEM8385003E080DGN
Config={ Fixed }
RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=0
BuffType=(0) unknown, BuffSize=0kB, MaxMultSect=16, MultSect=?1?
CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=156301488
IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120}
PIO modes: pio0 pio3 pio4
DMA modes: mdma0 mdma1 mdma2
UDMA modes: udma0 udma1 udma2
AdvancedPM=no WriteCache=enabled
Drive conforms to: ATA/ATAPI-7 T13 1532D rev.1: ATA/ATAPI-2 ATA/ATAPI-3 ATA/ATAPI-4 ATA/ATAPI-5 ATA/ATAPI-6 ATA/ATAPI-7
* current active mode
tytso@....edu wrote:
> On Sat, Mar 06, 2010 at 11:02:53PM +0100, Paul Chavent wrote:
>> Hello.
>>
>> I'm writing a real-time application that have to stream pictures to a SSD.
>>
>> The pictures are 640x480x1 pnm that are stored in one tar file. I
>> have one picture every 100ms.
>>
>> The problem is that the access (write) time (from a userspace point
>> of view) is not constant. I join you a piece of code that reproduce
>> the problem.
>
> What are you seeing/expecting? Here's what I'm getting with the X25-M
> Intel SSD:
>
> file size duration
>
> diff min : 3666548
> diff moy : 6639261
> diff max : 9429924
> 101 iterations
> major pagefaults : 0
> minor pagefaults : 0
>
> It's rarely if ever triggering your "suspect write" fprintf.
>
>> This leads me to ask the following questions : the solution to this
>> problem is
>>
>
> If you are seeing something seriously worse, you might want to test
> what happens if you write to the SSD directly; it may be the answer is
>
> (4) Buy a competently engineered SSD. :-)
>
> - Ted
> --
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>
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