atom feed21 messages in org.freebsd.freebsd-fsRe: Very inconsistent (read) speed on...
FromSent OnAttachments
Lev SerebryakovAug 30, 2011 12:10 pm 
Lev SerebryakovAug 30, 2011 12:17 pm 
Kirk McKusickAug 30, 2011 1:08 pm 
Lev SerebryakovAug 30, 2011 3:13 pm 
Lev SerebryakovAug 30, 2011 3:29 pm 
Lev SerebryakovAug 30, 2011 3:31 pm 
Bob FriesenhahnAug 30, 2011 3:39 pm 
Kirk McKusickAug 30, 2011 4:00 pm 
Jeremy ChadwickAug 30, 2011 5:42 pm 
Daniel KalchevAug 31, 2011 12:10 am 
Lev SerebryakovAug 31, 2011 12:38 am 
Lev SerebryakovAug 31, 2011 1:02 am 
Lev SerebryakovAug 31, 2011 1:10 am 
Lev SerebryakovAug 31, 2011 1:18 am 
Lev SerebryakovAug 31, 2011 1:36 am 
Daniel KalchevAug 31, 2011 1:48 am 
Lev SerebryakovAug 31, 2011 2:03 am 
Jeremy ChadwickAug 31, 2011 3:11 am 
Lev SerebryakovAug 31, 2011 4:36 am 
Daniel KalchevAug 31, 2011 4:46 am 
Lev SerebryakovAug 31, 2011 5:49 am 
Subject:Re: Very inconsistent (read) speed on UFS2
From:Lev Serebryakov (le@FreeBSD.org)
Date:Aug 31, 2011 2:03:21 am
List:org.freebsd.freebsd-fs

Hello, Daniel. You wrote 31 августа 2011 г., 12:48:32:

On 31.08.11 11:36, Lev Serebryakov wrote:

device r/s w/s kr/s kw/s wait svc_t %b ada1 340.9 292.9 43138.8 146.5 0 1.2 42 ada2 340.9 293.9 43138.8 147.0 0 1.9 63 ada3 340.9 292.9 43044.7 146.5 0 1.5 57 ada4 341.9 292.9 43232.9 146.5 0 1.3 42 ada5 341.9 292.0 43138.8 146.0 2 1.3 40

Very interesting, this writes. You need to find out what is causing these.

Yep. I've been very surprised by them.

Just some random thoughts:

This flapping may have something to do with the drives' internal caches. What are the drives?

WD20EARS, it is WD Green 2Tb, advanced format. Yes, I know, that they are not best performers at all, when here are seeks. It is why I don't expect good performance in random or multi-threaded (multi-client) access patterns here.

And, yes, I know about advanced format. Stripe size is 128Kb, and GEOM is built from raw drives, so all stripes are aligned. FS is created on raw GEOM, without any partitioning again, and block size is 32Kb, so everything should be aligned here too.

Really, if all reading speeds were, say, 120MiB/s, but every time and consistent, I don't start this thread. In case I would blame HDDs and my parsimony, but not software :)

SATA drives, unlike SAS have simplex communication with the host, that is, the drive cannot simultaneously read and write data and commands (from/to host). There might be some, perhaps locking contention in there? It is not contention for bandwidth obviously.

Yep...

In any case, you cannot measure read performance as long as it intermixes with writes, especially as you noted that your RAID5 code has some non-obvious write characteristics/optimizations.

I understand. Now I should understand how to pin down these writes.

-- // Black Lion AKA Lev Serebryakov <le@FreeBSD.org>

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