Re: IDE RAID controller and software raid in linux
On Wed, 2006-09-27 at 18:21 +0300, Rafi Gordon wrote:
> I made some more research on this topic.
> I am thinking of a solution using linux software RAID
> for disk crash.
> RAID 1 seems the best solution for this. (am I right?)
> It works with disk mirroring. This means that the data is in fact
> duplicated and written to both disks. This of course sets a high
> load on the CPU and the data buses.
Unless you are using a -
very- old machine (Pentium I/K5/K6), the CPU
load should be virtually invisible.
> So my question is:
> In practical terms, suppose we have 2 common 200 GB SATA-II disks (7200 RPM)
> buffer size 8MB, and about 8-10 ms average seek time for read/write
> (Or something like that). And suppose we have a 1GB RAM , on
> x86 (not 64 bit) with about 3GHZ CPU clock.
IMHO, I'd get a third 200GB disk and use RAID5. (Creating a second small
RAID1 setup just for /boot)
You should get better (read) performance at the price of a (slightly)
higher CPU load on write.
> And suppose we are NOT talking about servers but of a
> common linux programmer environment. (But on which a disk
> crash is unbearable and there is management which may afford
> another disk for that withouth hesitating).
All my development workstations (Both <at> work and <at> home) use a 3/4 disk
RAID5 configurations. In the past I had a number of IDE and SCSI disk
crashes and the machines never lost a heartbeat. At most, I suffered
from a minor performance degradation while the array was being rebuilt
in the background.
> Will it be bearable to use such a solution ?
> Or will the machine be so slow that it will be unbearable ?
Running on a 3.0Ghz CPU? You won't notice the RAID - even under severe
I/O and CPU loads.
> I simply cannot test Linux RAID 1 performance because
> it invloves erasing data and formattin to create a
> RAID set.
I just ran a short test (using hdparm) on one of my workstations (which
uses a 4 x 80GB 7.2K IDE setup):
/dev/md0: (/boot, 200MB)
Timing cached reads: 2552 MB in 2.00 seconds = 1276.89 MB/sec
Timing buffered disk reads: 98 MB in 2.03 seconds = 48.28 MB/sec
/dev/md1: (root, ~12GB)
Timing cached reads: 2848 MB in 2.00 seconds = 1423.99 MB/sec
Timing buffered disk reads: 296 MB in 3.01 seconds = 98.46 MB/sec
While hdparm is a poor benchmark tool, the 50MB/s (on the RAID1 based
boot) is fairly close to the maximum throughput of older 80GB IDE100
In short, you should expect better performance out of two 200GB SATA
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