[CentOS] SSD for Centos SWAP /tmp & /var/ partition

Benjamin Franz jfranz at freerun.com
Mon May 23 21:29:55 UTC 2011

On 05/23/2011 12:27 PM, Ray Van Dolson wrote:
>> Quote from
>> http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Storage_Administration_Guide/newmds-ssdtuning.html
>> :
>>      Red Hat also warns that software RAID levels 1, 4, 5, and 6 are not
>>      recommended for use on SSDs. During the initialization stage of these
>>      RAID levels, some RAID management utilities (such as mdadm) write to
>>      all of the blocks on the storage device to ensure that checksums
>>      operate properly. This will cause the performance of the SSD to degrade
>>      quickly.
> Huh.  Maybe LVM mirroring would be alright.

Not actually a problem if you are just using it for journaling. Journals 
max out at 400MB -  so you are using only a tiny fraction of the entire 
SSD for the journal while getting a large performance pop on small 
writes since the OS can safely return to you before the data is actually 
written to the slower magnetic disk. Another alternative is to *not use 
the entire SSD*. Deliberately leave say 25% or so unallocated. Kind of 
like short stroking a disk for performance: You sacrifice capacity for 

Benjamin Franz

Benjamin Franz

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