October 4th

larsmagne23

10 years ago

Dear Diary,

today was the day I was going to install a new SSD RAID system for the Gmane news spool. The old spool kinda ran full four months ago, but I kept deleting (and storing off-spool) the largest groups and waddled through.

I had one server that seemed like a good fit for the new news server: It had 8 physical disk slots. But the motherboard only had six SATA connectors, so I bought an LSI MegaRAID SAS 9240-8i card.

Installing the 2.5″ SSDs in a 3.5″ adapter. Five of the disks

I decided to add 2x 4TB spinning mechanical disks to the remaining two slots for, uhm, a search index perhaps?

All seven disks installed in their Supermicro caddies

Look at that gigantic hole, yearning to be filled.

Uhm… these captions took an odd turn back there…

I pull the server out of the rack and totally pop its top

Err… is that a photo of the RAID card? I think it might be…

The disk backplane had six slots already hooked up, so I viciously ripped three of the connectors out

And plugged five of the connectors from the RAID card back in

And then my biggest fans were reinstalled. Thank you thank you

Now the hardware was all installed, but getting to the LSI WebBIOS configuration was impossible.

I hit Ctrl+H repeatedly while booting, but I always just got the Linux boot prompt instead. I binged around a bit, and it turns out that if any other non-RAID disks are present in the system, the WebBIOS won’t appear at all.

So I popped the three spinning disks out of the machine, and presto:

I configured the RAID5 over the five 1TB SSDs. This would give me about 4TB, which is twice what the current news spool has.

However, building the RAID seems to take forever:

WTF? 2% in 20 minutes?

These are SATA3 SSDs. Read/write speed is over 500MB/s. That means that reading or writing a single disk should take under 30 minutes. Since the card can access all the disks independently, computing the RAID5 XOR shouldn’t take more than that.

But let’s be generous. Let’s say it has to read the disks sequentially, and write the parity disk sequentially. That’s 2.5 hours.

Instead it’s going to take 16 hours. WTF is up with that? Does the LSI MegaRAID SAS 9240-8i have the slowest CPU ever or something?

That’s just unbelievably slow.

Diary, I’m going to let it continue building the RAID and then do some speed tests. If it turns out that it’s this slow during operation, I’m going to rip it out and just do software RAID.