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I have Windows 2008 R2 SP1 with 4 identical SATA disks (Seagate Barracude 7200) in RAID 5 array. It has 4Gb of memory; all recent updates are installed. Problem: when I copy large file from one folder to another, I get about 10MB/s average speed. When I read this file from network share via 1Gbps connection - I get about 25-30 MB/s. Both numbers seems to be low for me - but specifically I'm very frustrated with low write speed.

there is no antivirus, no hyper-v, it's just a fileserver - i when i do my tests nobody else reads/write from it (we have only 4 people in a team, so I'm sure).

Not sure if that matters, but there is only 1 logic disk "C" with all available space (1400 GB).

I'm not an admin at all, so I have no idea where to look and what other information to provide. I did run performance monitor with "% idle time", "avg bytes read", "avg byte write" - here is the screenshot:

enter image description here

I'm not sure why there are such obvious spikes.

Any idea? Please let me know if you need me to provide more information - what counters should I check, etc. I'm very eager to get this solved.

Thank you.

UPDATE: we have another Windows 2008 R2 SP1 server with 2 RAID1 arrays - one is disk C (where windows is installed, another one is disk E). It is running Hyper-V and does not have antivirus. I noticed the following behavior when I copy large file (few GBs):

  1. C -> C: about 50MB/sec
  2. C -> E: about 55MB/sec
  3. E -> E: 8MB/sec!!!
  4. E -> C: 8MB/sec!!!

what could cause this?? E drive is RAID1 array from same Seagate Barracuda 1TB drives..

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    What kind of RAID controller?
    – Joel E Salas
    Apr 13, 2012 at 23:43
  • on both servers - Intel ICH10 built-in in main board.
    – avs099
    Apr 13, 2012 at 23:44

2 Answers 2

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Nearly all RAID5 implementations suffer from a write penalty. The short answer is: Never use RAID5, ever. The longer answer is, RAID 5 is useful in a select handful of cases where overall IOPS are not terribly important. When you're copying files to another folder, you're reading and writing to the same set of disks, which causes I/O contention greater than the sum of the cost of the operations. The reason is simple: It takes time for the disks to physically seek to the appropriate location on the disks.

Intel ICH10R is a type of "fake RAID," where the motherboard creates and maintains an array without the typical benefits of a dedicated processor and battery-backed cache. This generally does not perform well. A battery-backed cache (aka RAM) stores a number of operations and keeps you from thrashing your disks directly. To compound matters, 7.2K RPM SATA disks are also cheap and plentiful, but by no means perform well in a large-data environment.

In conclusion, you're pushing consumer hardware to its (realistic) limits. Make sure you have the absolute latest drivers, and take a serious look at buying a RAID card to help your ailing and slow storage system (note that you'll need to start from scratch, as RAID implementations are not inter-compatible).

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  • While I strongly disagree with your assertion that R5 should never be used (we use it extensively and don't have any of the problems you seem to think are unavoidable). The fake RAID is definitely the problem here. Intel and nVidia fake raid "chips" are notorious for horrid performance.
    – Chris S
    Apr 14, 2012 at 2:55
  • thank you, Joel. I'm looking at my options now - and looks like it's either cheap (below $100) RAID controller or software RAID. I know that both are not something hardcode admin would recommend - but if I have to choose between these 2 options, which one would you recommend?
    – avs099
    Apr 15, 2012 at 2:40
  • and one more question - what should I use instead of RAID5?
    – avs099
    Apr 15, 2012 at 2:40
  • Software RAID may fare better than fake RAID, but you'll have trouble getting Windows to boot from it. Buy a RAID card, you won't regret it. I highly recommend a RAID10 configuration for maximum read/write performance. Be sure to choose an appropriate stripe size (I recommend >=64K) and block size for the underlying filesystem.
    – Joel E Salas
    Apr 15, 2012 at 7:35
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Windows Raid is generally slow. Linux Raid is generally considered mature, better and faster. If you just need a file server I would just set up a Linux server with Samba to serve files for Linux/Win/Mac. I dont want to compare between Raid 1 to 10 because the have their own benifits and draw backs and should be chosen based on requirement.

Having said that its better to use H/w raid card than software/Bios/Fake Raid.

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  • The generalization is certainly inaccurate. The OPs problem is that he is suffering the RAID5 write penalty without the relief of a write-back cache. This would not be any better in Linux (or any other OS for that matter).
    – the-wabbit
    Sep 22, 2015 at 6:06

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