Am 12.02.10 18:17, schrieb Richard Elling:
On Feb 12, 2010, at 8:20 AM, Felix Buenemann wrote:
Hi Mickaël,
Am 12.02.10 13:49, schrieb Mickaël Maillot:
Intel X-25 M are MLC not SLC, there are very good for L2ARC.
Yes, I'm only using those for L2ARC, I'm planing on getting to Mtron Pro 7500
16GB SLC SSDs for ZIL.
and next, you need more RAM:
ZFS can't handle 4x 80 Gb of L2ARC with only 4Gb of RAM because ZFS
use memory to allocate and manage L2ARC.
Is there a guideline in which relation L2ARC size should be to RAM?
Approximately 200 bytes per record. I use the following example:
Suppose we use a Seagate LP 2 TByte disk for the L2ARC
+ Disk has 3,907,029,168 512 byte sectors, guaranteed
+ Workload uses 8 kByte fixed record size
RAM needed for arc_buf_hdr entries
+ Need = ~(3,907,029,168 - 9,232) * 200 / 16 = ~48 GBytes
Don't underestimate the RAM needed for large L2ARCs
I'm not sure how your workload record size plays into above formula
(where does - 9232 come from?), but given I've got ~300GB L2ARC, I'd
need about 7.2GB RAM, so upgrading to 8GB would be enough to satisfy the
L2ARC.
-- richard
I could upgrade the server to 8GB, but that's the maximum the i975X chipset can
handle.
Best Regards,
Felix Buenemann
- Felix
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