Intel Rapid Storage Technology raid1 slow speed

[Geremia]

Hello,

if anyone does not know, intel is advertising his chipset raid1 as double speeded in reading.
http://www.intel.com/support/chipsets/imsm/sb/CS-009337.htm

The performance of a RAID 1 array is greater than that of a single drive because data can be read from multiple disks - the original and the mirror - simultaneously. Disk writes do not realize the same benefit because data must first be written to one drive, then mirrored to the other.

I've observed a reading speed slower than one single disk alone, so i went investigating and posted some stuff on intel community forum.
http://communities.intel.com/message/172490

Anyone here interested in this stuff?

 

[groberts101]

sorry..don't have time to read those links right now.. but i will share this with you.

All Intel raids have write-back caching disabled by default. You'll need to manually enable it to receive max benefits frrom it. And unbeknownst to most.. reads are affected as well.

Hope that helps a bit.

 

[Geremia]

yes yes, i know, but i'm referring to reading, it does indeed read half data from one drive and the other half from the other, but seems rst falls sleeping and overall speed is worse than a single drive.
Have a deep reading

 

[SolMiester]

wow, Intel are very quiet on this!

 

[greenhawk]

wow, Intel are very quiet on this!

depends on how you want to measure it. With raid 1, you generally want both drives read from, then have the data compaired to ensure the data is good. Reading it as mentioned looses that benifit.

Secondly, others besides intel have had this feature over the years. IIRC gigabyte called it raid 1.5 or something like that.

You still only have the space of one drive so not a advantage for those wanting a fast system. Still better to just get a single SSD than go looking for odd raid configurations.

 

[Geremia]

I'm not talking about what generally someone wants or think, i'm talking about what the intel RST exactly does in raid1: reads half from a disk and another half from the other disk.
If both disks are mirrored and array is healty, intel RST does not care to compare data of both disks during reading, it just trust them, because:
- if ata write command went good, it means no bad sector or any other failure occured, so trust stays on.
ok, you may occur in a situation where sector have been correctly writed, but after some time you can't read it anymore, so trust=off, array status bad, it will read sector from the other disk.
As addictional feature, it does alternate the sector chunks reading, let me explain:
let's say it reads in chunks of 128 sectors, let's say "odd chunks" from disk0, "even chnks" from disk1 (this is what happens in raid0).
To help bad sectors finding, after some chunks read, it swaps odd with even, i mean, odd chunks are then read from disk1 and even chunks from disk1.
This alternating thing will result in a chunk being read both from disk0 and disk1 after some repetitive reading of the same data, so, it does not read data from both disks everytime (like generally thought), but after some time it is quite sure it had occasion to read the same sector from both disks. but yes, it didn't compare both data to be the same, it just trusts the good writing and the good reading

 

[poupou18]

Hello,

if anyone does not know, intel is advertising his chipset raid1 as double speeded in reading.
http://www.intel.com/support/chipsets/imsm/sb/CS-009337.htm


I've observed a reading speed slower than one single disk alone, so i went investigating and posted some stuff on intel community forum.
http://communities.intel.com/message/172490

Anyone here interested in this stuff?

Hello Geremia,

I've checked on many intel ICHxxR motherboard and I found that reading from a RAID 1 array is not faster than reading from a standalone HDD.

It seems to be a faulty description by INTEL !
So INTEL seems to be a liar when they say that :

The performance of a RAID 1 array is greater than that of a single drive because data can be read from multiple disks - the original and the mirror - simultaneously. Disk writes do not realize the same benefit because data must first be written to one drive, then mirrored to the other.

But maybe there is something do to improve RAID 1 array by Intel chipset ???

Best regards,

 

[poupou18]

depends on how you want to measure it. With raid 1, you generally want both drives read from, then have the data compaired to ensure the data is good. Reading it as mentioned looses that benifit.

Hello greenhawk,

Intel website clearly states that reading from a RAID 1 array should be faster than reading from a standalone HDD...
So, the problem is not to do what you want (and not everyone will want the same things) but that INTEL's chipset do what INTEL say it will do !

And INTEL says :

The performance of a RAID 1 array is greater than that of a single drive because data can be read from multiple disks - the original and the mirror - simultaneously. Disk writes do not realize the same benefit because data must first be written to one drive, then mirrored to the other.

but they don't do it !!!

Best regards,