Poor SSD Raid1 performance

[holgihero]

Hi all,i know, software raid is not supported but maybe someone has an idea on how to solve this:
I have a fresh install of prxmox on a HP Proliant ML110 G7 with data (LVM) on a Raid1 located on two SSD Samsung 840Pro 512G.
Everything seemed fine after creating md0 on /dev/sdb and /dev/sdd but after syncronisation finished performance is very poor.
I get io waits up to 80%.

atop shows that one of the disks is very slow, the other one looks good
DSK | sdd | busy 81% | read 36 | write 384 | KiB/r 29 | KiB/w 128 | MBr/s 0.10 | MBw/s 4.81 | avq 2.79 | avio 22.4 ms |
DSK | sdb | busy 17% | read 915 | write 381 | KiB/r 41 | KiB/w 129 | MBr/s 3.68 | MBw/s 4.81 | avq 3.24 | avio 1.49 ms |

DSK | sdd | busy 96% | read 13 | write 158 | KiB/r 8 | KiB/w 167 | MBr/s 0.01 | MBw/s 2.58 | avq 6.42 | avio 58.4 ms |
DSK | sdb | busy 7% | read 74 | write 164 | KiB/r 18 | KiB/w 164 | MBr/s 0.13 | MBw/s 2.64 | avq 3.97 | avio 3.18 ms |

So one of the disks is about 10 times slower than the other.Any idea?

Best regards, Holger

 

[udo]

Hi all,i know, software raid is not supported but maybe someone has an idea on how to solve this:
I have a fresh install of prxmox on a HP Proliant ML110 G7 with data (LVM) on a Raid1 located on two SSD Samsung 840Pro 512G.
Everything seemed fine after creating md0 on /dev/sdb and /dev/sdd but after syncronisation finished performance is very poor.
I get io waits up to 80%.

atop shows that one of the disks is very slow, the other one looks good
DSK | sdd | busy 81% | read 36 | write 384 | KiB/r 29 | KiB/w 128 | MBr/s 0.10 | MBw/s 4.81 | avq 2.79 | avio 22.4 ms |
DSK | sdb | busy 17% | read 915 | write 381 | KiB/r 41 | KiB/w 129 | MBr/s 3.68 | MBw/s 4.81 | avq 3.24 | avio 1.49 ms |

DSK | sdd | busy 96% | read 13 | write 158 | KiB/r 8 | KiB/w 167 | MBr/s 0.01 | MBw/s 2.58 | avq 6.42 | avio 58.4 ms |
DSK | sdb | busy 7% | read 74 | write 164 | KiB/r 18 | KiB/w 164 | MBr/s 0.13 | MBw/s 2.64 | avq 3.97 | avio 3.18 ms |

So one of the disks is about 10 times slower than the other.Any idea?

Best regards, Holger

Hi,
perhaps not the right bios config? ide/sata/ahci

Or firmware-trouble on the SSDs? with the actual firmware (840 pro) some laptops have huge problems!

Udo

 

[holgihero]

Hi,
perhaps not the right bios config? ide/sata/ahci

Or firmware-trouble on the SSDs? with the actual firmware (840 pro) some laptops have huge problems!

Udo

I'm in contact with HP support. They suggest updating every firmware, but also they advise that SSDs are not certified for that server. Nevertheless we have two mechanical disks and two SSD in the system of which one mechanical and one SSD have slow performance.
Debian shows nothing wrong...
I'll check bios tomorrow.

Best regards, Holger

 

[holgihero]

Problem found: Disk has no overprovisioning activated.

As statet here: http://www.samsung.com/global/business/semiconductor/minisite/SSD/us/html/about/whitepaper05.html
"Samsung has chosen to implement a minimum amount of OP in its mainstream drives (the 840 PRO will not feature mandatory OP)"

When mirroring disk a to disk b finished, the disk controller regarded the whole disk b as completely filled with data and therefore we noticed a huge drop in performance.

Conclusion: Dont use the complete SSD for a raid 1 or equivalent. Or use disks with factory implemented overprovisioning (and check that in advance ).

Best regards, Holger