March 9th, 2012

Dear Diary,

I’ve switched the SSD disks back to the LSI MegaRAID SAS 9260-8i controller again, and did some final benchmarks.

I’m comparing reading bits of the Gmane spool in semi-random (i.e. ext4 directory) order, name order (which is also the same order as the files were created), and finally, just reading a big hunking file.  I’ve done this on a spinning disk, with soft RAID, and with the MegaRAID. The last two are over five Samsung 830 512GB in RAID5 mode.

  Semi-random order Name order Sequential reads
Spinning disk 234 files/s 2 MB/s 6062 files/s 48 MB/s 130 MB/s
Soft RAID5 over SSDs 4076 files/s 32 MB/s 8103 files/s 64 MB/s 264 MB/s
LSI MegaRAID SAS 9260-8i over SSDs 4564 files/s 36 MB/s 18708 files/s 148 MB/s 580 MB/s 

So, for the thing that matters — semi-random reads — we get a 20x improvement going from spinning magnetic disks to SSD.  However, the difference between using soft RAID over SATA2.0 versus using that spiffy MegaRAID SATA3.0 card isn’t very thrilling in my realistic use case.  

However, being able to read the 19K files per second when I’m doing, say, re-indexing or statistical analysis, will certainly be nice.  I’ll probably not get that speed when the machine is under load and serving out messages at the same time, but it’ll be a lot better than a contested spinning disk.

So to conclude:  The LSI MegaRAID 9260-8i was a waste of time and money.  I should just have soft RAID-ed the thing, as was my original plan.  But since I’ve got the card now, I might as well just use it.

I’ve now started the real syncing of the entire spool to the new machine.  That’ll probably take a few days, but I’m aiming for replacing the Gmane news server with the new machine sometime next week.  This will hopefully mean the end of all those “load over 16” login denials.

And, Diary, since it seems that some people are able to hack into you and read my most secret thoughts, I’m going to go back to writing you with a quill pen on parchment again.  Surely Google won’t be able to access you there.

6 thoughts on “March 9th, 2012”

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s