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On 08/02/11 16:00, taemun wrote:
> It's generally accepted that two things can break a ZFS pool: the use of
> non-ECC RAM; and storage devices which do not respect cache flushes. You're
> aiming for a system which is likely to have both. The latter by virtue of
> the fact that most USB <=> SATA controllers often don't respect sync
> requests. Both of these can lead to broken metadata/uberblocks and hence a
> broken pool.
Caché flushes are important. The fist step I do when getting a new
computer&disk is to write a small program (like 5 lines long) to write
small (1 byte) data followed by a "fsync". If the number of fsyncs per
second is too high, I know I can't trust the disk.
Python code:
"""
import os, time
syncs = 10000
f = open("zz","w")
t = time.time()
for i in xrange(syncs) :
f.write("a")
f.flush()
os.fsync(f)
print "Realizamos %d transacciones por segundo" %(syncs/(time.time()-t))
"""
Using 7200 RPM disks, the right value is around 120 transactions per
second. If the value is far higher, "somebody" is lying to you about
caché flushes.
- --
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