[DRBD-user] drbd on top of hardware raid

Lars Ellenberg Lars.Ellenberg at linbit.com
Wed Aug 9 22:27:30 CEST 2006

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

/ 2006-08-09 13:53:39 -0600
\ Monty Taylor:
> No, it's an internal LSI MegaRAID configured in Raid5. (not my choice)
> On the positive side, though, it supports 90M/sec of reading.

if it is an option, try to put it into jbod,
then do software raid5 on those.
should help if that controller is "CPU" bound,
and your file server is not...

and, btw, you probably know that already ...
raid controllers tend to pretend against the kernel that data was
on stable storage, even when they indeed only have it still in their
write back cache.
if that cache is battery backed, ok.
if not, and you get data corruption after blackout/brownout,
don't blame linux, nor the device/file system drivers,
nor drbd either...

unfortunately sometimes you can not put it in "write through" mode
(use that cache, but only say its done when its really done), but
only switch off the cache completely.
and then your write throughput gets really bad...

so you better make sure you run on some ups, and monitor it,
and power down the box cleanly in case the ups capacity runs out.

: Lars Ellenberg                                  Tel +43-1-8178292-0  :
: LINBIT Information Technologies GmbH            Fax +43-1-8178292-82 :
: Schoenbrunner Str. 244, A-1120 Vienna/Europe   http://www.linbit.com :
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