Ubuntu 10.04

I have a Samsung F3R drive (SATA II) connected to my motherboard via a Kingwin hot swappable tray.

My current write speeds for extended sequential write are 40.4 Kbs/s! This was verified via a dd write from /dev/zero.

This drive is formatted with ext4.

I've narrowed it down to what I believe is the fstab options. Please give me your thoughts.

Would the sync option cause such awful performance?


My trouble shooting that has led me to this point:

Poor performance with amanda backup: Test drive speed from shell
dd if=/dev/zero of=/backups/writetest bs=512 count=2000000 : ~40Kb/s
swap out drive (mounted explicitly to /mnt): write speed of 198Mb/s (same dd command)
replace original drive (mounted explicitly to /mnt): write speed of 128 Mb/s (same dd command)
mount the current (problematic) HDD via fstab options (listed above) i.e. "mount /backups": 40 Kb/s write speed (same dd command)

Thanks for your help,
WT

Are there any errors/informations in the /var/log/messages file?

Is SMART enabled? Do you have the ability to use the 'smartctl' program to do any testing? It can verify the drives integrity, performance, etc...

Hi there,

Yes, you are going in the write direction sync option is used when you want a command to immediately write the changes to disk. This option is good when you are dealing with floppy or usb drive in which you do not want the data write to take place afterwards.

When you issue a command to copy or move system caches it and write to the disk whenever it gets free time. If you use sync option it forces the system to write the changes to the disk immediately.

Use async instead of sync and then see how it goes.

Also is this happened recently or it is like that from the beginning. If it is from beginning I would also suggest checking SATA drive jumper setting.

OK, after testing the async option in the fstab, write speed is: 111 Mb/s

So the question becomes, is there a way I can write synchronously to the hdd and have some reasonable performance?


While async is not a deal-breaker, it seems better to get the backups onto disk immediately, instead of waiting for a sync. I have no idea when the kernel syncs, so it may just be my ignorance.

WT

I will give you an example:

If I issue cp command to copy some xyz file to USB then kernel keep that in cache and if you remove the USB without issuing umount command then that data might be lost but if you issue umount command before removing USB then kernel will first write data which is in cache to USB and then umount the device.

I hope this will make things clear.