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I am trying to get a raid 10 running with LSI 9260-8i (IBM M5015) and 4 x Samsung 850 Pro 512GB SSDs.

The problem is, that the resulting sequential write performance is really bad (< 100MB/s). With raid 0, it is > 800 MB/s.

My system is a Dell Precision T5500 with 2 x Intel Xeon X5675 3,06 GHz 6 Core, 72 GB RAM, running proxmox 5.1-51 on debian stretch.

These are my raid-parameters:

Strip size 64 KB Read Policy: No Read Ahead IO Policy: Direct IO Default Write Policy: Write Through Default Access Policy: RW

Enabling Disk Cache makes no difference with the write performance.

I created a thin lvm on the raid 10 for storing raw-images with IO thread enabled. On a virtual machine, the read performance is > 800 MB/s and with raid 0, i don't have the problem with low write performance.

What might be the problem?

  • Did you fill 100% of the physical capacity back then when you were writing to the RAID0? This is where TRIM would become crucial. Welcome to the site. – kubanczyk May 1 '18 at 22:59
  • I am not shure, what you mean. I am using write through, if that is, what you mean. And no caching ahead - so everything will be directly written to the disk. – DonCanalie May 2 '18 at 7:59
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Sorry, that gen of cards aren't super high performing even with SSD's

Look to the 12G sas raid cards, they are built with SSD performance in mind.

However one thing that might be a problem to normal performance --- do you have the battery for the bbwc hooked up and is it charged? No battery, no performance

  • No, i have no battery. I will get one and try, if it works better. The problem with the 12G sas raid card may be, that the pcie support of the motherboard is too bad... – DonCanalie May 1 '18 at 23:27
  • Yes, once you will have the battery, you will be able to change Read policy to "Read ahead" and Write policy to "Write Back" to improve sequential patterns for write performance. – batistuta09 May 3 '18 at 7:50
  • For SSDs, it is best practice to use write through and no read ahed. so i don't need the battery. But i found the problem. I bought two of the SSDs second hand. When i tested them seperately, i found that they had a sequential write throughput of ~40MB/s. I handed them back and ordered some new ones. so never buy second hand SSDs :-D – DonCanalie May 4 '18 at 17:04

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